S everal advancements have been made in the topical management of cutaneous epithelial malignancies, including actinic keratosis (AK), superficial basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) in situ. Due to variability in clinical presentations and specific patient-related factors, therapy must be individualized. The availability of multiple therapeutic options including medical and surgical approaches allows the physician to select and combine modalities effectively. The following reviews newer topical agents, such as diclofenac 3% gel (Solaraze) and imiquimod 5% cream (Aldara). Comparing the Topical Agents for AKs The major currently available topical agents for treatment of AKs, 5-fluorouracil (Carac, Efudex), diclofenac and imiquimod, induce their effects through different modes of action. It is important to conceptualize the differences between these topical agents in order to better understand treatment expectations and clinical outcomes, including the anticipated uncomfortable cytotoxic reaction with 5-fluorouracil, the variable erythematous inflammatory response with imiquimod and the low-grade erythema with diclofenac. With rare exception, symptomatology associated with diclofenac or imiquimod use is significantly less than with 5-fluorouracil, a fact that is understandable once one considers the cytotoxic mode of action of the latter agent. The differences in the mechanisms of action of these agents help to explain their clinical nuances (see figure 1 at below). Newer Topical Options For Actinic Keratoses Topical Diclofenac. Diclofenac 3% gel (Solaraze) is FDA approved for treatment of AK. Diclofenac is a non-steroidal, anti-inflammatory agent (NSAID), which modulates arachidonic acid metabolism through inhibition of cyclooxygenase (COX).1 Reduction in formation of arachidonic acid metabolites has been correlated with reduced carcinogenicity, enhanced immune surveillance and reduced angiogenesis.1,2 In addition, experimental studies suggest a correlation between COX-2 overexpression and carcinogenesis. COX-2 upregulation occurs in response to ultraviolet-B irradiation of human skin with associated dysplasia. Increased COX and COX-mediated prostaglandin E2 has been linked with photodamaged skin and AK. And, overexpression of COX-2 has been noted in SCC.1,3,4 Multiple controlled studies have evaluated the efficacy and safety of topical diclofenac applied twice daily for AKs. Dosage-duration finding analysis (n = 291) based on double-blind, controlled trials with topical diclofenac suggest that a 90-day duration of therapy is optimal, although some patients may exhibit complete or partial lesion clearance with 30 to 60 days of use (see “Diclofenac 3% Gel” table below).1,5 Anatomic sites of AK involvement that were evaluated in the studies include scalp, forehead, central face and dorsum of the hands. Complete clearance of AK lesions was noted in half of the patients treated for 90 days and in one-third of the patients treated for 30 to 60 days; the corresponding responses in the vehicle-treated groups were 19% and 10%, respectively. In the trial where topical diclofenac was used for 30 to 60 days, a 50% to 65% reduction in lesions was observed. Seventy-nine percent of patients treated for 90 days demonstrated complete or marked clearance. In patients not demonstrating complete clearance, a decrease in the number of AKs and a reduction in the emergence of new AK lesions was noted by investigators.1,5,6 Data from a 90-day, multi-center, open-label trial (n = 67) of topical diclofenac applied twice daily reports that 85% of patients demonstrated >75% lesion clearance and 58% exhibited complete lesion clearance.7 Although patients may experience some degree of local inflammation and erythema at sites of topical diclofenac application, the extent and severity are mild and tolerable in the majority of patients and were markedly less than the application site reactions experienced with cryotherapy or topical 5-fluorouracil; no serious adverse reactions have been reported.6 Topical Imiquimod. Topical imiquimod is an “immune response facilitator” that appears to effectively treat both viral disorders (human papillomavirus infection, molluscum contagiosum) and some cutaneous malignancies (AK, SCC in situ, superficial BCC) by augmenting both innate and acquired immune response.6,8 The effective use of topical imiquimod for treatment of AKs has been extensively reviewed in a previous issue of this journal (February 2003) by the author and in other recent publications.6,8,9 Currently, topical imiquimod is under evaluation by the FDA for approval for AK treatment. It is generally recommended that imiquimod therapy for AK be initiated with nightly application 3 times per week. The usual duration required to achieve reasonable efficacy is 6 weeks to 8 weeks with longer durations (12 weeks to 16 weeks) utilized if warranted based on clinical response. As imiquimod induces lymphocytic infiltration targeted to the region of AK involvement after drug application, a visible inflammatory response is usually observed. When the response is visibly brisk, a rest period off of therapy (1 week to 4 weeks) is often recommended followed by reinitiation of therapy if AK lesions persist. In most cases of local brisk inflammation associated with imiquimod use, symptomatology is minimal.6,8 The concept of cycle therapy (4 weeks on, 4 weeks off) has been evaluated in an open-label study (n = 25) of topical imiquimod applied 3 times per week (during on cycles) with 46% of individual anatomic regions (scalp, cheek, forehead, temple) completely cleared after the first cycle and an additional 36% cleared after the second cycle.10 Cycle therapy allows for “built-in” rest periods to allow time for resolution of inflammation. Understanding of Imiquimod Mechanism of Action Application of topical imiquimod to cutaneous epithelial malignancies, such as AK, BCC and SCC in situ, has been shown to induce a “directed immune response” at the site of application. In association with the production of a Th-1 lymphocyte cytokine pattern, antigen-specific lymphocytes are recruited to the focus of disease where drug is applied.11-13 The visible clinical response is characterized by inflammation, which may range from low-grade to brisk.8 As the inflammatory response represents the accumulation of T lymphocytes directed against specific disease antigen, the visible inflammation that is produced reflects therapeutic activity and has been termed “cytokine dermatitis.”8 In cases associated with a complete absence of inflammation, a lack of therapeutic response should be considered. Topical imiquimod is capable of stimulating a cytokine profile similar to what has been demonstrated with eradication of basal cell carcinoma induced by intralesional interferon or spontaneous tumor regression.11-22 Although the mechanisms by which topical imiquimod produces clinical and histologic clearance of cutaneous epithelial malignancies (BCC, AK and SCC in situ) are not fully understood, several observations based on multiple studies appear to relate to the efficacy of imiquimod use. Most imiquimod mechanism of action studies for treatment of cutaneous malignancy have focused on BCC as the tumor model. Observations include: • Reversal of BCC Escape Mechanisms.8,14-18,20-23 Basal cell carcinomas frequently avoid “spontaneous” immune eradication by the host due to several “escape mechanisms,” such as inhibition of ICAM (adhesion molecule) expression, expression of Bcl-2 protein, which inhibits tumor cell apoptosis, expression of interleukin-10 (IL-10), which may promote immunosuppression and development of suppressor T lymphocytes, surface expression of Fas-ligand (Fas-L, CD 95L), which may “kill” T lymphocytes expressing Fas antigen receptors (Fas-R, CD 95) and lack of expression of Fas-R on tumor cells resulting in avoidance of apoptosis and tumor survival. Topical imiquimod reverses several of the above BCC escape mechanisms by enhancing dermal endothelial ICAM-1 expression, decreasing Bcl-2 expression, allowing for increased susceptibility of BCC cells to apoptosis, increasing infiltration with T helper lymphocytes and promoting expression of Fas-R on BCC cells, leading to apoptosis of tumor through interaction with Fas-L receptors present on infiltrating T lymphocytes or adjacent tumor cells (“BCC suicide”). • Altered Peritumoral Inflammation.8,14-20,21-23 Careful histologic evaluation of BCCs frequently demonstrates peritumoral lymphocytic infiltrates that surround but do not invade tumor islands. In these infiltrates, T helper lymphocytes (CD4+ T cells) are scant, suggesting limited cell-mediated immune response against tumor cells. Increased interferon(IFN)-gamma enhances infiltration of T helper lymphocytes, which may promote apoptosis of tumor cells through Fas-R~Fas-L interaction. Cytotoxic T cells also require the assistance of T helper cells. Current evidence indicates that topically applied imiquimod enhances cell-mediated response against specific disorders, such as BCC, due to indirect stimulation of IFN-gamma production along with a Th-1 (cell-mediated) lymphocyte cytokine pattern (IFN-alpha, IL-12, IL-18). • Enhanced Antigen Presentation.8,11-15,17-19,24,25 Imiquimod activates epidermal dendritic cells (Langerhans cells) involved in antigen presentation and enhances their migration to regional lymph nodes. Within regional lymph nodes, antigen is presented to naïve T lymphocytes (Th-0 cells), which are “converted” to activated T lymphocytes. The activated “antigen specific” T lymphocytes are then recruited into the circulation, ultimating infiltrating the site of disease (antigen target). Dendritic cells exposed to imiquimod demonstrate the ability to enhance IFN-gamma production by peripheral blood mononuclear cells and secretion by T lymphocytes. • Enhancement of Specific Types of Infiltrating T Lymphocytes.8,14-21 As compared to vehicle-treated tumors, BCCs treated with topical imiquimod exhibit a dense mononuclear cell infiltrate. Immunostaining after application of imiquimod demonstrates a predominance of T helper lymphocytes. Natural killer (NK) cells (CD56+ cells) represent 25% of the peritumoral infiltrate after use of imiquimod with little, if any, positive staining observed for B lymphocytes (CD20+ cells). • Enhanced Innate Immune Response Early During Treatment.26 One study histologically analyzed BCCs before and after treatment with topical imiquimod upon clinical signs of erosion after daily application for 5 to 8 days. Results suggest that imiquimod stimulates epidermal and dermal plasmacytoid dendritic cells to release proinflammatory cytokines including interferons. Recruitment of innate immune cells, such as macrophages, invade epidermis, preceding T cell activation. A variety of upregulated genes were identified after imiquimod use, including a collection of genes enhanced by IFN-alpha, and potent upregulation of genes involved in pathways of apoptotic signaling. Epidermal erosion was predominantly related to infiltration with cells of macrophage origin (CD68+ cells), mostly neutrophils. This study suggested that T cell activation may play a secondary role in eradication of tumors cells after the initial activity provided by the innate immune response. • Toll-like Receptor Binding.12,14,15 Toll-like receptors (TLRs) are a family of cell surface proteins, expressed on dendritic cells, which serve as vital components of innate and adaptive immune response. The extracellular domain of the receptor binds to specific ligands, most of which are microbial in origin. Once TLR~ligand interaction occurs, the cytoplasmic domain of the receptor signals nuclear gene expression related to a specific immune response. Thus far, 11 TLRs have been identified, each apparently specific for detecting individual pathogens. For example, exoproducts of Propionibacterium acnes have been shown to bind with TLR-2, an interaction correlated with inflammation in acne vulgaris. Interestingly, at achievable concentrations after topical application, imiquimod behaves as a “serendipitous ligand” for TLR-7. TLR-7 activation by imiquimod enhances antigen presentation and activation signaling between dendritic cells and T lymphocytes through increased expression of costimulatory molecules and certain major histocompatibility complex molecules that are required to complete antigen processing. Ultimately, a bridge between innate and adaptive (cell-mediated) immunity is provided by TLR-7 activation. • Promotion of Apoptosis.17,18,22,23 BCCs lack surface Fas antigen receptors (Fas-R) allowing them to avoid interaction with Fas-L receptors on the surfaces of T lymphocytes infiltrating around the tumor. As a result, BCC cells escape apoptosis and subsequent tumor destruction. Imiquimod promotes expression of Fas-R on BCC cell surfaces, leading to apoptosis of tumor through interaction with Fas-L receptors present on infiltrating T lymphocytes or adjacent tumor cells (“BCC suicide”). Clinical Experience with Imiquimod for Superficial BCC Currently available data with topical imiquimod for treatment of superficial BCC suggest application 5 to 7 days per week for 6 to 12 weeks.8,20,27,28 Once daily application in two studies (n = 227) produced nearly identical BCC clearance rates of 87.9% and 87.1%.20,27,28 A duration of 6 weeks is likely to be sufficient in many patients.8 Upon development of brisk inflammation, a rest period (1 to 4 weeks off therapy) is frequently recommended, followed by reinitiation of therapy.8,20 Ultimately, the duration of therapy is determined by the intensity of inflammation correlated with clinical response.8 In addition, as superficial BCCs sometimes contain nodular foci, it is significant that topical imiquimod has demonstrated efficacy for both superficial and nodular disease.8,29 Clinical Experience with Imiquimod for SCC In Situ Multiple reports have confirmed the efficacy of topical imiquimod for the treatment of SCC in situ.8,30-36 An initial trial evaluating topical imiquimod for SCC in situ applied once daily for up to 16 weeks confirmed a 93% cure rate with post-treatment biopsy completed after 6 weeks and clinical follow-up completed over 6 months.30 Lesion size ranged from 1 cm to 5.4 cm with >90% located on the legs. In six patients developing brisk inflammation, complete clearance occurred after 4 to 8 weeks of imiquimod use. This suggests that the intensity and/or nature of the targeted inflammatory response plays a major role in inducing a therapeutic effect and may be a more important factor than strict adherence to a course of treatment.8 Two cases of SCC in situ (leg, shoulder) and one case of superficially invasive SCC (nose tip) treated with imiquimod applied nightly for 6 weeks cleared completely based on clinical assessment and biopsy at 1 month post-treatment. One patient required a 2-week rest period due to development of a marked inflammatory response.35 Earlier case reports of SCC in situ have documented efficacy with imiquimod application 3 times per week for durations ranging from 9 to 17 weeks; post-treatment follow-ups have indicated no evidence of recurrence over a range of 12 to 15 months.31-33 Five additional cases of penile SCC in situ treated with topical imiquimod every second day for 9 to 16 weeks demonstrated complete clearance confirmed by post-treatment biopsy and clinical evaluation over durations of 3 months in one patient and 12 months in four patients.36 Based on available data, imiquimod therapy for SCC in situ should be initiated at a frequency of three applications per week.8 Frequency and duration of therapy may then be adjusted based on clinical response and intensity of inflammation.8 As with therapy for BCC, the overall healing responses and cosmetic results are favorable. Case Report The following case exemplifies practical application of topical imiquimod for treatment of SCC in situ. A 68-year-old Caucasian male presented with two adjacent biopsy proven thin plaques of SCC in situ involving the left posterior temple region (Photo 1). The area of clinical involvement inclusive of both lesions measured 2.6 cm in greatest diameter. After discussion of treatment options, benefits and risks, therapy was initiated with topical imiquimod applied 3 nights weekly. After 4 weeks of therapy, the patient returned for follow-up (Photo 2). Although brisk inflammation, superficial erosion and crusting were noted, the patient experienced only mild pruritus and no discomfort. A 3-week rest period was recommended after which time the inflammation subsided with only mild residual erythema (Photo 3). Imiquimod therapy was restarted at the same frequency for 2 more weeks. Follow-up 2 weeks after stopping therapy revealed complete visible and palpable clearance of SCC in situ, no signs of residual inflammation and no treatment-related complications (Photo 4). The patient declined post-treatment biopsy and was instructed regarding periodic clinical follow-up.
Cutaneous Epithelial Malignancies
S everal advancements have been made in the topical management of cutaneous epithelial malignancies, including actinic keratosis (AK), superficial basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) in situ. Due to variability in clinical presentations and specific patient-related factors, therapy must be individualized. The availability of multiple therapeutic options including medical and surgical approaches allows the physician to select and combine modalities effectively. The following reviews newer topical agents, such as diclofenac 3% gel (Solaraze) and imiquimod 5% cream (Aldara). Comparing the Topical Agents for AKs The major currently available topical agents for treatment of AKs, 5-fluorouracil (Carac, Efudex), diclofenac and imiquimod, induce their effects through different modes of action. It is important to conceptualize the differences between these topical agents in order to better understand treatment expectations and clinical outcomes, including the anticipated uncomfortable cytotoxic reaction with 5-fluorouracil, the variable erythematous inflammatory response with imiquimod and the low-grade erythema with diclofenac. With rare exception, symptomatology associated with diclofenac or imiquimod use is significantly less than with 5-fluorouracil, a fact that is understandable once one considers the cytotoxic mode of action of the latter agent. The differences in the mechanisms of action of these agents help to explain their clinical nuances (see figure 1 at below). Newer Topical Options For Actinic Keratoses Topical Diclofenac. Diclofenac 3% gel (Solaraze) is FDA approved for treatment of AK. Diclofenac is a non-steroidal, anti-inflammatory agent (NSAID), which modulates arachidonic acid metabolism through inhibition of cyclooxygenase (COX).1 Reduction in formation of arachidonic acid metabolites has been correlated with reduced carcinogenicity, enhanced immune surveillance and reduced angiogenesis.1,2 In addition, experimental studies suggest a correlation between COX-2 overexpression and carcinogenesis. COX-2 upregulation occurs in response to ultraviolet-B irradiation of human skin with associated dysplasia. Increased COX and COX-mediated prostaglandin E2 has been linked with photodamaged skin and AK. And, overexpression of COX-2 has been noted in SCC.1,3,4 Multiple controlled studies have evaluated the efficacy and safety of topical diclofenac applied twice daily for AKs. Dosage-duration finding analysis (n = 291) based on double-blind, controlled trials with topical diclofenac suggest that a 90-day duration of therapy is optimal, although some patients may exhibit complete or partial lesion clearance with 30 to 60 days of use (see “Diclofenac 3% Gel” table below).1,5 Anatomic sites of AK involvement that were evaluated in the studies include scalp, forehead, central face and dorsum of the hands. Complete clearance of AK lesions was noted in half of the patients treated for 90 days and in one-third of the patients treated for 30 to 60 days; the corresponding responses in the vehicle-treated groups were 19% and 10%, respectively. In the trial where topical diclofenac was used for 30 to 60 days, a 50% to 65% reduction in lesions was observed. Seventy-nine percent of patients treated for 90 days demonstrated complete or marked clearance. In patients not demonstrating complete clearance, a decrease in the number of AKs and a reduction in the emergence of new AK lesions was noted by investigators.1,5,6 Data from a 90-day, multi-center, open-label trial (n = 67) of topical diclofenac applied twice daily reports that 85% of patients demonstrated >75% lesion clearance and 58% exhibited complete lesion clearance.7 Although patients may experience some degree of local inflammation and erythema at sites of topical diclofenac application, the extent and severity are mild and tolerable in the majority of patients and were markedly less than the application site reactions experienced with cryotherapy or topical 5-fluorouracil; no serious adverse reactions have been reported.6 Topical Imiquimod. Topical imiquimod is an “immune response facilitator” that appears to effectively treat both viral disorders (human papillomavirus infection, molluscum contagiosum) and some cutaneous malignancies (AK, SCC in situ, superficial BCC) by augmenting both innate and acquired immune response.6,8 The effective use of topical imiquimod for treatment of AKs has been extensively reviewed in a previous issue of this journal (February 2003) by the author and in other recent publications.6,8,9 Currently, topical imiquimod is under evaluation by the FDA for approval for AK treatment. It is generally recommended that imiquimod therapy for AK be initiated with nightly application 3 times per week. The usual duration required to achieve reasonable efficacy is 6 weeks to 8 weeks with longer durations (12 weeks to 16 weeks) utilized if warranted based on clinical response. As imiquimod induces lymphocytic infiltration targeted to the region of AK involvement after drug application, a visible inflammatory response is usually observed. When the response is visibly brisk, a rest period off of therapy (1 week to 4 weeks) is often recommended followed by reinitiation of therapy if AK lesions persist. In most cases of local brisk inflammation associated with imiquimod use, symptomatology is minimal.6,8 The concept of cycle therapy (4 weeks on, 4 weeks off) has been evaluated in an open-label study (n = 25) of topical imiquimod applied 3 times per week (during on cycles) with 46% of individual anatomic regions (scalp, cheek, forehead, temple) completely cleared after the first cycle and an additional 36% cleared after the second cycle.10 Cycle therapy allows for “built-in” rest periods to allow time for resolution of inflammation. Understanding of Imiquimod Mechanism of Action Application of topical imiquimod to cutaneous epithelial malignancies, such as AK, BCC and SCC in situ, has been shown to induce a “directed immune response” at the site of application. In association with the production of a Th-1 lymphocyte cytokine pattern, antigen-specific lymphocytes are recruited to the focus of disease where drug is applied.11-13 The visible clinical response is characterized by inflammation, which may range from low-grade to brisk.8 As the inflammatory response represents the accumulation of T lymphocytes directed against specific disease antigen, the visible inflammation that is produced reflects therapeutic activity and has been termed “cytokine dermatitis.”8 In cases associated with a complete absence of inflammation, a lack of therapeutic response should be considered. Topical imiquimod is capable of stimulating a cytokine profile similar to what has been demonstrated with eradication of basal cell carcinoma induced by intralesional interferon or spontaneous tumor regression.11-22 Although the mechanisms by which topical imiquimod produces clinical and histologic clearance of cutaneous epithelial malignancies (BCC, AK and SCC in situ) are not fully understood, several observations based on multiple studies appear to relate to the efficacy of imiquimod use. Most imiquimod mechanism of action studies for treatment of cutaneous malignancy have focused on BCC as the tumor model. Observations include: • Reversal of BCC Escape Mechanisms.8,14-18,20-23 Basal cell carcinomas frequently avoid “spontaneous” immune eradication by the host due to several “escape mechanisms,” such as inhibition of ICAM (adhesion molecule) expression, expression of Bcl-2 protein, which inhibits tumor cell apoptosis, expression of interleukin-10 (IL-10), which may promote immunosuppression and development of suppressor T lymphocytes, surface expression of Fas-ligand (Fas-L, CD 95L), which may “kill” T lymphocytes expressing Fas antigen receptors (Fas-R, CD 95) and lack of expression of Fas-R on tumor cells resulting in avoidance of apoptosis and tumor survival. Topical imiquimod reverses several of the above BCC escape mechanisms by enhancing dermal endothelial ICAM-1 expression, decreasing Bcl-2 expression, allowing for increased susceptibility of BCC cells to apoptosis, increasing infiltration with T helper lymphocytes and promoting expression of Fas-R on BCC cells, leading to apoptosis of tumor through interaction with Fas-L receptors present on infiltrating T lymphocytes or adjacent tumor cells (“BCC suicide”). • Altered Peritumoral Inflammation.8,14-20,21-23 Careful histologic evaluation of BCCs frequently demonstrates peritumoral lymphocytic infiltrates that surround but do not invade tumor islands. In these infiltrates, T helper lymphocytes (CD4+ T cells) are scant, suggesting limited cell-mediated immune response against tumor cells. Increased interferon(IFN)-gamma enhances infiltration of T helper lymphocytes, which may promote apoptosis of tumor cells through Fas-R~Fas-L interaction. Cytotoxic T cells also require the assistance of T helper cells. Current evidence indicates that topically applied imiquimod enhances cell-mediated response against specific disorders, such as BCC, due to indirect stimulation of IFN-gamma production along with a Th-1 (cell-mediated) lymphocyte cytokine pattern (IFN-alpha, IL-12, IL-18). • Enhanced Antigen Presentation.8,11-15,17-19,24,25 Imiquimod activates epidermal dendritic cells (Langerhans cells) involved in antigen presentation and enhances their migration to regional lymph nodes. Within regional lymph nodes, antigen is presented to naïve T lymphocytes (Th-0 cells), which are “converted” to activated T lymphocytes. The activated “antigen specific” T lymphocytes are then recruited into the circulation, ultimating infiltrating the site of disease (antigen target). Dendritic cells exposed to imiquimod demonstrate the ability to enhance IFN-gamma production by peripheral blood mononuclear cells and secretion by T lymphocytes. • Enhancement of Specific Types of Infiltrating T Lymphocytes.8,14-21 As compared to vehicle-treated tumors, BCCs treated with topical imiquimod exhibit a dense mononuclear cell infiltrate. Immunostaining after application of imiquimod demonstrates a predominance of T helper lymphocytes. Natural killer (NK) cells (CD56+ cells) represent 25% of the peritumoral infiltrate after use of imiquimod with little, if any, positive staining observed for B lymphocytes (CD20+ cells). • Enhanced Innate Immune Response Early During Treatment.26 One study histologically analyzed BCCs before and after treatment with topical imiquimod upon clinical signs of erosion after daily application for 5 to 8 days. Results suggest that imiquimod stimulates epidermal and dermal plasmacytoid dendritic cells to release proinflammatory cytokines including interferons. Recruitment of innate immune cells, such as macrophages, invade epidermis, preceding T cell activation. A variety of upregulated genes were identified after imiquimod use, including a collection of genes enhanced by IFN-alpha, and potent upregulation of genes involved in pathways of apoptotic signaling. Epidermal erosion was predominantly related to infiltration with cells of macrophage origin (CD68+ cells), mostly neutrophils. This study suggested that T cell activation may play a secondary role in eradication of tumors cells after the initial activity provided by the innate immune response. • Toll-like Receptor Binding.12,14,15 Toll-like receptors (TLRs) are a family of cell surface proteins, expressed on dendritic cells, which serve as vital components of innate and adaptive immune response. The extracellular domain of the receptor binds to specific ligands, most of which are microbial in origin. Once TLR~ligand interaction occurs, the cytoplasmic domain of the receptor signals nuclear gene expression related to a specific immune response. Thus far, 11 TLRs have been identified, each apparently specific for detecting individual pathogens. For example, exoproducts of Propionibacterium acnes have been shown to bind with TLR-2, an interaction correlated with inflammation in acne vulgaris. Interestingly, at achievable concentrations after topical application, imiquimod behaves as a “serendipitous ligand” for TLR-7. TLR-7 activation by imiquimod enhances antigen presentation and activation signaling between dendritic cells and T lymphocytes through increased expression of costimulatory molecules and certain major histocompatibility complex molecules that are required to complete antigen processing. Ultimately, a bridge between innate and adaptive (cell-mediated) immunity is provided by TLR-7 activation. • Promotion of Apoptosis.17,18,22,23 BCCs lack surface Fas antigen receptors (Fas-R) allowing them to avoid interaction with Fas-L receptors on the surfaces of T lymphocytes infiltrating around the tumor. As a result, BCC cells escape apoptosis and subsequent tumor destruction. Imiquimod promotes expression of Fas-R on BCC cell surfaces, leading to apoptosis of tumor through interaction with Fas-L receptors present on infiltrating T lymphocytes or adjacent tumor cells (“BCC suicide”). Clinical Experience with Imiquimod for Superficial BCC Currently available data with topical imiquimod for treatment of superficial BCC suggest application 5 to 7 days per week for 6 to 12 weeks.8,20,27,28 Once daily application in two studies (n = 227) produced nearly identical BCC clearance rates of 87.9% and 87.1%.20,27,28 A duration of 6 weeks is likely to be sufficient in many patients.8 Upon development of brisk inflammation, a rest period (1 to 4 weeks off therapy) is frequently recommended, followed by reinitiation of therapy.8,20 Ultimately, the duration of therapy is determined by the intensity of inflammation correlated with clinical response.8 In addition, as superficial BCCs sometimes contain nodular foci, it is significant that topical imiquimod has demonstrated efficacy for both superficial and nodular disease.8,29 Clinical Experience with Imiquimod for SCC In Situ Multiple reports have confirmed the efficacy of topical imiquimod for the treatment of SCC in situ.8,30-36 An initial trial evaluating topical imiquimod for SCC in situ applied once daily for up to 16 weeks confirmed a 93% cure rate with post-treatment biopsy completed after 6 weeks and clinical follow-up completed over 6 months.30 Lesion size ranged from 1 cm to 5.4 cm with >90% located on the legs. In six patients developing brisk inflammation, complete clearance occurred after 4 to 8 weeks of imiquimod use. This suggests that the intensity and/or nature of the targeted inflammatory response plays a major role in inducing a therapeutic effect and may be a more important factor than strict adherence to a course of treatment.8 Two cases of SCC in situ (leg, shoulder) and one case of superficially invasive SCC (nose tip) treated with imiquimod applied nightly for 6 weeks cleared completely based on clinical assessment and biopsy at 1 month post-treatment. One patient required a 2-week rest period due to development of a marked inflammatory response.35 Earlier case reports of SCC in situ have documented efficacy with imiquimod application 3 times per week for durations ranging from 9 to 17 weeks; post-treatment follow-ups have indicated no evidence of recurrence over a range of 12 to 15 months.31-33 Five additional cases of penile SCC in situ treated with topical imiquimod every second day for 9 to 16 weeks demonstrated complete clearance confirmed by post-treatment biopsy and clinical evaluation over durations of 3 months in one patient and 12 months in four patients.36 Based on available data, imiquimod therapy for SCC in situ should be initiated at a frequency of three applications per week.8 Frequency and duration of therapy may then be adjusted based on clinical response and intensity of inflammation.8 As with therapy for BCC, the overall healing responses and cosmetic results are favorable. Case Report The following case exemplifies practical application of topical imiquimod for treatment of SCC in situ. A 68-year-old Caucasian male presented with two adjacent biopsy proven thin plaques of SCC in situ involving the left posterior temple region (Photo 1). The area of clinical involvement inclusive of both lesions measured 2.6 cm in greatest diameter. After discussion of treatment options, benefits and risks, therapy was initiated with topical imiquimod applied 3 nights weekly. After 4 weeks of therapy, the patient returned for follow-up (Photo 2). Although brisk inflammation, superficial erosion and crusting were noted, the patient experienced only mild pruritus and no discomfort. A 3-week rest period was recommended after which time the inflammation subsided with only mild residual erythema (Photo 3). Imiquimod therapy was restarted at the same frequency for 2 more weeks. Follow-up 2 weeks after stopping therapy revealed complete visible and palpable clearance of SCC in situ, no signs of residual inflammation and no treatment-related complications (Photo 4). The patient declined post-treatment biopsy and was instructed regarding periodic clinical follow-up.
S everal advancements have been made in the topical management of cutaneous epithelial malignancies, including actinic keratosis (AK), superficial basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) in situ. Due to variability in clinical presentations and specific patient-related factors, therapy must be individualized. The availability of multiple therapeutic options including medical and surgical approaches allows the physician to select and combine modalities effectively. The following reviews newer topical agents, such as diclofenac 3% gel (Solaraze) and imiquimod 5% cream (Aldara). Comparing the Topical Agents for AKs The major currently available topical agents for treatment of AKs, 5-fluorouracil (Carac, Efudex), diclofenac and imiquimod, induce their effects through different modes of action. It is important to conceptualize the differences between these topical agents in order to better understand treatment expectations and clinical outcomes, including the anticipated uncomfortable cytotoxic reaction with 5-fluorouracil, the variable erythematous inflammatory response with imiquimod and the low-grade erythema with diclofenac. With rare exception, symptomatology associated with diclofenac or imiquimod use is significantly less than with 5-fluorouracil, a fact that is understandable once one considers the cytotoxic mode of action of the latter agent. The differences in the mechanisms of action of these agents help to explain their clinical nuances (see figure 1 at below). Newer Topical Options For Actinic Keratoses Topical Diclofenac. Diclofenac 3% gel (Solaraze) is FDA approved for treatment of AK. Diclofenac is a non-steroidal, anti-inflammatory agent (NSAID), which modulates arachidonic acid metabolism through inhibition of cyclooxygenase (COX).1 Reduction in formation of arachidonic acid metabolites has been correlated with reduced carcinogenicity, enhanced immune surveillance and reduced angiogenesis.1,2 In addition, experimental studies suggest a correlation between COX-2 overexpression and carcinogenesis. COX-2 upregulation occurs in response to ultraviolet-B irradiation of human skin with associated dysplasia. Increased COX and COX-mediated prostaglandin E2 has been linked with photodamaged skin and AK. And, overexpression of COX-2 has been noted in SCC.1,3,4 Multiple controlled studies have evaluated the efficacy and safety of topical diclofenac applied twice daily for AKs. Dosage-duration finding analysis (n = 291) based on double-blind, controlled trials with topical diclofenac suggest that a 90-day duration of therapy is optimal, although some patients may exhibit complete or partial lesion clearance with 30 to 60 days of use (see “Diclofenac 3% Gel” table below).1,5 Anatomic sites of AK involvement that were evaluated in the studies include scalp, forehead, central face and dorsum of the hands. Complete clearance of AK lesions was noted in half of the patients treated for 90 days and in one-third of the patients treated for 30 to 60 days; the corresponding responses in the vehicle-treated groups were 19% and 10%, respectively. In the trial where topical diclofenac was used for 30 to 60 days, a 50% to 65% reduction in lesions was observed. Seventy-nine percent of patients treated for 90 days demonstrated complete or marked clearance. In patients not demonstrating complete clearance, a decrease in the number of AKs and a reduction in the emergence of new AK lesions was noted by investigators.1,5,6 Data from a 90-day, multi-center, open-label trial (n = 67) of topical diclofenac applied twice daily reports that 85% of patients demonstrated >75% lesion clearance and 58% exhibited complete lesion clearance.7 Although patients may experience some degree of local inflammation and erythema at sites of topical diclofenac application, the extent and severity are mild and tolerable in the majority of patients and were markedly less than the application site reactions experienced with cryotherapy or topical 5-fluorouracil; no serious adverse reactions have been reported.6 Topical Imiquimod. Topical imiquimod is an “immune response facilitator” that appears to effectively treat both viral disorders (human papillomavirus infection, molluscum contagiosum) and some cutaneous malignancies (AK, SCC in situ, superficial BCC) by augmenting both innate and acquired immune response.6,8 The effective use of topical imiquimod for treatment of AKs has been extensively reviewed in a previous issue of this journal (February 2003) by the author and in other recent publications.6,8,9 Currently, topical imiquimod is under evaluation by the FDA for approval for AK treatment. It is generally recommended that imiquimod therapy for AK be initiated with nightly application 3 times per week. The usual duration required to achieve reasonable efficacy is 6 weeks to 8 weeks with longer durations (12 weeks to 16 weeks) utilized if warranted based on clinical response. As imiquimod induces lymphocytic infiltration targeted to the region of AK involvement after drug application, a visible inflammatory response is usually observed. When the response is visibly brisk, a rest period off of therapy (1 week to 4 weeks) is often recommended followed by reinitiation of therapy if AK lesions persist. In most cases of local brisk inflammation associated with imiquimod use, symptomatology is minimal.6,8 The concept of cycle therapy (4 weeks on, 4 weeks off) has been evaluated in an open-label study (n = 25) of topical imiquimod applied 3 times per week (during on cycles) with 46% of individual anatomic regions (scalp, cheek, forehead, temple) completely cleared after the first cycle and an additional 36% cleared after the second cycle.10 Cycle therapy allows for “built-in” rest periods to allow time for resolution of inflammation. Understanding of Imiquimod Mechanism of Action Application of topical imiquimod to cutaneous epithelial malignancies, such as AK, BCC and SCC in situ, has been shown to induce a “directed immune response” at the site of application. In association with the production of a Th-1 lymphocyte cytokine pattern, antigen-specific lymphocytes are recruited to the focus of disease where drug is applied.11-13 The visible clinical response is characterized by inflammation, which may range from low-grade to brisk.8 As the inflammatory response represents the accumulation of T lymphocytes directed against specific disease antigen, the visible inflammation that is produced reflects therapeutic activity and has been termed “cytokine dermatitis.”8 In cases associated with a complete absence of inflammation, a lack of therapeutic response should be considered. Topical imiquimod is capable of stimulating a cytokine profile similar to what has been demonstrated with eradication of basal cell carcinoma induced by intralesional interferon or spontaneous tumor regression.11-22 Although the mechanisms by which topical imiquimod produces clinical and histologic clearance of cutaneous epithelial malignancies (BCC, AK and SCC in situ) are not fully understood, several observations based on multiple studies appear to relate to the efficacy of imiquimod use. Most imiquimod mechanism of action studies for treatment of cutaneous malignancy have focused on BCC as the tumor model. Observations include: • Reversal of BCC Escape Mechanisms.8,14-18,20-23 Basal cell carcinomas frequently avoid “spontaneous” immune eradication by the host due to several “escape mechanisms,” such as inhibition of ICAM (adhesion molecule) expression, expression of Bcl-2 protein, which inhibits tumor cell apoptosis, expression of interleukin-10 (IL-10), which may promote immunosuppression and development of suppressor T lymphocytes, surface expression of Fas-ligand (Fas-L, CD 95L), which may “kill” T lymphocytes expressing Fas antigen receptors (Fas-R, CD 95) and lack of expression of Fas-R on tumor cells resulting in avoidance of apoptosis and tumor survival. Topical imiquimod reverses several of the above BCC escape mechanisms by enhancing dermal endothelial ICAM-1 expression, decreasing Bcl-2 expression, allowing for increased susceptibility of BCC cells to apoptosis, increasing infiltration with T helper lymphocytes and promoting expression of Fas-R on BCC cells, leading to apoptosis of tumor through interaction with Fas-L receptors present on infiltrating T lymphocytes or adjacent tumor cells (“BCC suicide”). • Altered Peritumoral Inflammation.8,14-20,21-23 Careful histologic evaluation of BCCs frequently demonstrates peritumoral lymphocytic infiltrates that surround but do not invade tumor islands. In these infiltrates, T helper lymphocytes (CD4+ T cells) are scant, suggesting limited cell-mediated immune response against tumor cells. Increased interferon(IFN)-gamma enhances infiltration of T helper lymphocytes, which may promote apoptosis of tumor cells through Fas-R~Fas-L interaction. Cytotoxic T cells also require the assistance of T helper cells. Current evidence indicates that topically applied imiquimod enhances cell-mediated response against specific disorders, such as BCC, due to indirect stimulation of IFN-gamma production along with a Th-1 (cell-mediated) lymphocyte cytokine pattern (IFN-alpha, IL-12, IL-18). • Enhanced Antigen Presentation.8,11-15,17-19,24,25 Imiquimod activates epidermal dendritic cells (Langerhans cells) involved in antigen presentation and enhances their migration to regional lymph nodes. Within regional lymph nodes, antigen is presented to naïve T lymphocytes (Th-0 cells), which are “converted” to activated T lymphocytes. The activated “antigen specific” T lymphocytes are then recruited into the circulation, ultimating infiltrating the site of disease (antigen target). Dendritic cells exposed to imiquimod demonstrate the ability to enhance IFN-gamma production by peripheral blood mononuclear cells and secretion by T lymphocytes. • Enhancement of Specific Types of Infiltrating T Lymphocytes.8,14-21 As compared to vehicle-treated tumors, BCCs treated with topical imiquimod exhibit a dense mononuclear cell infiltrate. Immunostaining after application of imiquimod demonstrates a predominance of T helper lymphocytes. Natural killer (NK) cells (CD56+ cells) represent 25% of the peritumoral infiltrate after use of imiquimod with little, if any, positive staining observed for B lymphocytes (CD20+ cells). • Enhanced Innate Immune Response Early During Treatment.26 One study histologically analyzed BCCs before and after treatment with topical imiquimod upon clinical signs of erosion after daily application for 5 to 8 days. Results suggest that imiquimod stimulates epidermal and dermal plasmacytoid dendritic cells to release proinflammatory cytokines including interferons. Recruitment of innate immune cells, such as macrophages, invade epidermis, preceding T cell activation. A variety of upregulated genes were identified after imiquimod use, including a collection of genes enhanced by IFN-alpha, and potent upregulation of genes involved in pathways of apoptotic signaling. Epidermal erosion was predominantly related to infiltration with cells of macrophage origin (CD68+ cells), mostly neutrophils. This study suggested that T cell activation may play a secondary role in eradication of tumors cells after the initial activity provided by the innate immune response. • Toll-like Receptor Binding.12,14,15 Toll-like receptors (TLRs) are a family of cell surface proteins, expressed on dendritic cells, which serve as vital components of innate and adaptive immune response. The extracellular domain of the receptor binds to specific ligands, most of which are microbial in origin. Once TLR~ligand interaction occurs, the cytoplasmic domain of the receptor signals nuclear gene expression related to a specific immune response. Thus far, 11 TLRs have been identified, each apparently specific for detecting individual pathogens. For example, exoproducts of Propionibacterium acnes have been shown to bind with TLR-2, an interaction correlated with inflammation in acne vulgaris. Interestingly, at achievable concentrations after topical application, imiquimod behaves as a “serendipitous ligand” for TLR-7. TLR-7 activation by imiquimod enhances antigen presentation and activation signaling between dendritic cells and T lymphocytes through increased expression of costimulatory molecules and certain major histocompatibility complex molecules that are required to complete antigen processing. Ultimately, a bridge between innate and adaptive (cell-mediated) immunity is provided by TLR-7 activation. • Promotion of Apoptosis.17,18,22,23 BCCs lack surface Fas antigen receptors (Fas-R) allowing them to avoid interaction with Fas-L receptors on the surfaces of T lymphocytes infiltrating around the tumor. As a result, BCC cells escape apoptosis and subsequent tumor destruction. Imiquimod promotes expression of Fas-R on BCC cell surfaces, leading to apoptosis of tumor through interaction with Fas-L receptors present on infiltrating T lymphocytes or adjacent tumor cells (“BCC suicide”). Clinical Experience with Imiquimod for Superficial BCC Currently available data with topical imiquimod for treatment of superficial BCC suggest application 5 to 7 days per week for 6 to 12 weeks.8,20,27,28 Once daily application in two studies (n = 227) produced nearly identical BCC clearance rates of 87.9% and 87.1%.20,27,28 A duration of 6 weeks is likely to be sufficient in many patients.8 Upon development of brisk inflammation, a rest period (1 to 4 weeks off therapy) is frequently recommended, followed by reinitiation of therapy.8,20 Ultimately, the duration of therapy is determined by the intensity of inflammation correlated with clinical response.8 In addition, as superficial BCCs sometimes contain nodular foci, it is significant that topical imiquimod has demonstrated efficacy for both superficial and nodular disease.8,29 Clinical Experience with Imiquimod for SCC In Situ Multiple reports have confirmed the efficacy of topical imiquimod for the treatment of SCC in situ.8,30-36 An initial trial evaluating topical imiquimod for SCC in situ applied once daily for up to 16 weeks confirmed a 93% cure rate with post-treatment biopsy completed after 6 weeks and clinical follow-up completed over 6 months.30 Lesion size ranged from 1 cm to 5.4 cm with >90% located on the legs. In six patients developing brisk inflammation, complete clearance occurred after 4 to 8 weeks of imiquimod use. This suggests that the intensity and/or nature of the targeted inflammatory response plays a major role in inducing a therapeutic effect and may be a more important factor than strict adherence to a course of treatment.8 Two cases of SCC in situ (leg, shoulder) and one case of superficially invasive SCC (nose tip) treated with imiquimod applied nightly for 6 weeks cleared completely based on clinical assessment and biopsy at 1 month post-treatment. One patient required a 2-week rest period due to development of a marked inflammatory response.35 Earlier case reports of SCC in situ have documented efficacy with imiquimod application 3 times per week for durations ranging from 9 to 17 weeks; post-treatment follow-ups have indicated no evidence of recurrence over a range of 12 to 15 months.31-33 Five additional cases of penile SCC in situ treated with topical imiquimod every second day for 9 to 16 weeks demonstrated complete clearance confirmed by post-treatment biopsy and clinical evaluation over durations of 3 months in one patient and 12 months in four patients.36 Based on available data, imiquimod therapy for SCC in situ should be initiated at a frequency of three applications per week.8 Frequency and duration of therapy may then be adjusted based on clinical response and intensity of inflammation.8 As with therapy for BCC, the overall healing responses and cosmetic results are favorable. Case Report The following case exemplifies practical application of topical imiquimod for treatment of SCC in situ. A 68-year-old Caucasian male presented with two adjacent biopsy proven thin plaques of SCC in situ involving the left posterior temple region (Photo 1). The area of clinical involvement inclusive of both lesions measured 2.6 cm in greatest diameter. After discussion of treatment options, benefits and risks, therapy was initiated with topical imiquimod applied 3 nights weekly. After 4 weeks of therapy, the patient returned for follow-up (Photo 2). Although brisk inflammation, superficial erosion and crusting were noted, the patient experienced only mild pruritus and no discomfort. A 3-week rest period was recommended after which time the inflammation subsided with only mild residual erythema (Photo 3). Imiquimod therapy was restarted at the same frequency for 2 more weeks. Follow-up 2 weeks after stopping therapy revealed complete visible and palpable clearance of SCC in situ, no signs of residual inflammation and no treatment-related complications (Photo 4). The patient declined post-treatment biopsy and was instructed regarding periodic clinical follow-up.
