What Is This Nodular Lesion on the Upper Back?

Derm Dx

What Is This Nodular Lesion on the Upper Back?

Shealinna Ge, MD, PGY3

and Amor Khachemoune, MD, FAAD, FACMS-Section Editor

February 2022

Case Report

A 75-year-old man with a 3-year history of a slow growing “cyst” on the upper back presented to his dermatologist because the lesion has become painful. The patient denied any history of local trauma. The rest of his medical and surgical histories were noncontributory. On skin examination, there was a 3.2- × 2.2-cm, somewhat circumscribed, indurated, and deep-seated nodule with a central pearly smooth-surfaced erythematous protruded papule with arborizing telangiectasia on the paraspinal right upper back (Figures 1, 2). A clinical diagnosis of an infiltrative keratinocyte neoplasm was suspected, and a deep tangential biopsy was performed.

What Is The Diagnosis?

Keep scrolling for the answer!

Diagnosis:

Superficial Leiomyosarcoma

Superficial leiomyosarcomas are primary leiomyosarcomas arising from the skin. It is a rare neoplasm of smooth muscle of unknown etiology¹ representing approximately 3% to 6.5% of soft tissue sarcomas^2-4 and make up 7% to 10% of all leiomyosarcomas.^5,6 Most superficial leiomyosarcomas are sporadic tumors with mutations in the TP53 or CDKN2A genes.^7,8 Most lesions arise de novo, but leiomyosarcomas have been reported to arise from benign leiomyomas, scars, and even nevus sebaceous.^9-11 They have also been observed in patients with Reed syndrome,¹²Li Fraumeni syndrome,¹³ and HIV with Epstein-Barr virus reactivation.^14,15

Superficial leiomyosarcomas are subcategorized into cutaneous and subcutaneous lesions. Cutaneous leiomyosarcoma are derived from arrector pili muscles and originated in the dermis with extension into the subcutaneous tissue, whereas subcutaneous leiomyosarcomas arise from vascular smooth muscles of adipose tissue and tend to be larger and more aggressive.^1,16 Subcutaneous leiomyosarcomas are more likely to present on the extremities compared with cutaneous lesions (62% vs 33%), which are more commonly found on the head and neck.^17-20 While the metastatic potential of superficial leiomyosarcomas is low, these tumors demonstrate aggressive growth and local destruction. Additionally, there is a 25% to 37% recurrence rate for superficial leiomyosarcomas after treatment and close follow up is recommended.

Clinical Presentation and Histopathology

Superficial leiomyosarcomas are often misdiagnosed. They most commonly present as skin-colored nodules with nonspecific features, leading to a wide range of differential diagnoses including fibromas, neurofibromas, dermatofibromas, lipomas, intradermal nevi, and cysts.²² Recently, dermoscopy has been used to evaluate superficial leiomyosarcomas. However, superficial leiomyosarcoma can mimic common cutaneous tumors such as basal cell carcinomas, squamous cell carcinomas, dermatofibromas, and melanomas even with dermoscopic evaluation.^4,22 The most common vascular patterns on dermoscopy are linear, irregular, arborizing, or polymorphic.³ Occasionally, white structures, milky red areas, ulceration, and even pigment networks can also be appreciated.^{3, 23-25}

Diagnosis requires histopathologic evaluation. Atypical spindle-shaped cells with cigar-like nuclei can be observed in fascicles on hematoxylin-eosin (H&E) stain. The most common growth patterns of superficial leiomyosarcomas are nodular and diffuse. The nodular pattern is characterized by high cellularity, more mitosis, and necrosis whereas the diffuse pattern is characterized by low cellularity, fewer mitosis, and lack of necrosis.²⁶ Smooth muscle actin and vimentin stains are positive in most cases, but desmin is only expressed in about 60% of superficial leiomyosarcomas.²⁶

Differential Diagnosis

The most common differential diagnoses are described in the eTable.

Treatment

Treatment is most often wide local excision, but the recommended margins of 2 cm to 5 cm can pose reconstructive challenges.²⁷ More recently, Mohs micrographic surgery has gained popularity for treatment of leiomyosarcoma due to superior margin control, tissue sparing, and lowering recurrence rates to 2% to 14%.^5,28,29

Our Patient

A deep shave biopsy was performed by his primary dermatologist due to concerns for keratinocyte carcinoma. The biopsy sample demonstrated a dermal neoplasm composed of interlacing bundles of apparent smooth muscle fibers intermingled with various amounts of collagen bundles. The spindle-shaped cells were thin with blunted edges and long nuclei, some with subnuclear vacuoles, some with enlarged and hyperchromatic nuclei, and arranged in intersecting fascicles. A few mitotic figures were observed on all sections examined. The overlying epidermis showed mild acanthosis (Figures 3, 4). The spindle-shaped cells expressed smooth muscle actin. There was also some weak staining of desmin focally and Ki67 in scattered cells. Staining for S100, SOX10, CD68, AE1/3, and CK903 were negative.

The patient underwent wide local excision with a 3-cm margin outside of the infiltrative area and deep to the fascia with complete clearance of the tumor (Figure 5).

Conclusion

Superficial leiomyosarcoma is a rare tumor of smooth muscle origin that is difficult to diagnose due to similarities in its clinical and dermoscopic presentations as other cutaneous neoplasms. Diagnosis often requires clinicohistopathological correlation and staining is strongly recommended with high degree of suspicion. The standard treatment is wide local excision with a 2- to 5-cm margin, but Mohs micrographic surgery is becoming increasingly popular for treatment of superficial leiomyosarcoma.

Acknowledgement

We extend our appreciation to Dr Amir Zahir, who assisted with the history and evaluation of the manuscript.

Dr Ge is a dermatologist in the department of dermatology at University of Maryland Medical Center in Baltimore, MD. Dr Khachemoune is on faculty at the Veterans Affairs Hospital and SUNY Down-state Dermatology Service in Brooklyn, NY.

Disclosure: The authors report no relevant financial relationships.

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