Radiofrequency Ablation of Vertebral Alveolar Soft Part Sarcoma Metastasis With the STAR Tumor Ablation System After Attempted Palliation With External Beam Radiation

Abstract: Alveolar soft part sarcoma is a rare malignancy that is known to be resistant to radiation therapy and chemotherapy. The traditional methods are (1) vertebral debulking with or without stabilization and (2) irradiation. The STAR Tumor Ablation System (DFINE) allows for a minimally invasive, single-access procedure that demonstrates significant pain relief in vertebral metastases where traditional palliation methods fall short. This case illustrates a role for radiofrequency ablation therapy of a radioresistant tumor that failed stereotactic body radiation therapy resulting in significant pain relief and bulk tumor reduction.  

Key words: tumor ablation, spine tumor, radiofrequency ablation

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A 22-year-old female presented with intractable lumbar pain secondary to stage IV alveolar soft part sarcoma (ASPS) originating from the right psoas muscle with metastases to the brain and lumbar spine. She had lumbar and radicular pain in the right lower extremity rated with an 8 out of 10 visual analog scale (VAS) score. Six months prior to presentation, she underwent stereotactic body radiation therapy (SBRT) to the L2 to L5 vertebrae, receiving 37.5 Gy in 15 fractions using an anterior-posterior/posterior-anterior (AP/PA) field. Following SBRT, she experienced radiation dermatitis and refractory nausea with less than desirable pain relief without narcotics. Cross-sectional CT demonstrated lytic tumors in the L3 and L4 vertebrae (Figure 1).

Magnetic resonance imaging demonstrated tumor in the L4 vertebrae with mass effect, narrowing the spinal canal, displacing the thecal sac (Figure 2) and encroaching upon the right L4-L5 neural foramen (Figure 3). Additional palliative external beam radiation was considered a less desirable option for the pain relapse, and interventional radiology was consulted for percutaneous radiofrequency ablation (RFA) of the tumor in L4.

Treatment of the L4 Lesion

The STAR Tumor Ablation System (DFINE) was inserted into the tumor at L4. 

The device was positioned such that the ablation field included the maximum amount of tumor while sparing the sensitive neurologic structures nearby (Figures 4 and 5). The SpineSTAR Ablation Instrument articulates in a way that allows it to be positioned within the tumor in multiple areas for overlapping fields while using only one access site. The flexibility with positioning combined with the two thermocouple sensors allows for accurate prediction of the ablation zone and helps avoid damage to critical structures.

Bone cement was applied after the ablation. The patient’s pain score decreased from 8/10 prior to the procedure to 5/10 immediately post procedure, and then to a score of 0/10 2 months later. At 6 months post procedure she remains pain free from the L4 tumor. Magnetic resonance imaging of the lumbar spine was obtained 6 days post STAR procedure, which demonstrated debulking of the tumor resulting in decrease mass effect on the spinal canal (Figure 6) and right L4-L5 neural foramen (Figure 7). 

Discussion

Alveolar soft part sarcomas are rare, highly malignant tumors typically occurring in adolescent and younger adult patients. The lower extremities, female genital tract, head and neck are the most common locations. Alveolar soft part sarcoma comprises less than 1% of sarcomas while sarcomas comprise about 1% of all newly diagnosed cancers, and 15% of all childhood cancers. The prognosis of stage IV ASPS is poor. Complete surgical resection of all tumors is the key of successful treatment of stage IV ASPS. Though local recurrence is rarely seen, distant metastasis is frequently observed. Metastasis has been reported as long as 15 years after initial resection of the tumor. The lungs, bones, the central nervous system, and the liver are the most common sites of metastasis. No survival advantage was observed when adding adjuvant radiotherapy and/or chemotherapy. Currently, there is an ongoing clinical trial of Cediranib in the treatment of patients with ASPS (https://clinicaltrials.gov/ct2/show/NCT01391962).

Radiofrequency ablation treats tumors by delivery of thermal energy causing tissue necrosis of the tumor. Predictors of success are tumor size and tumor location. For most thermal ablative techniques, tumors up to 4 cm in size can be easily treated with adequate margin, approximately 1 cm, provided that they are not abutting a large blood vessel, the heart, or any other vital organ that could not be safely included in the ablation zone. High electrical conductivity and low tissue impedance limit the effectiveness of RF ablation. Radiofrequency ablation is contraindicated in patients with heart pacemakers or other electronic device implants. The STAR procedure is also contraindicated in vertebral levels C1 to C7.

Palliation of vertebral metastasis of radioresistant tumors with traditional methods can be difficult. 

While external beam radiation therapy is the gold standard for palliation of spine metastasis, this case illustrates a role for RFA therapy of a radioresistant tumor that failed SBRT. 

Neurosurgical interventions and SBRT for painful vertebral lesions can involve substantial morbidity. Neurosurgical debulking and stabilization is invasive and has a complication rate approaching 13%.¹ A multi-institution study showed that after spine SBRT, 13.9% of cases involved either a de novo vertebral compression fracture or progression of a prior fracture.² Radiation therapy also has common side effects, such as nausea and skin irritation, both of which led to increased hospitalization time for this patient after her initial SBRT course. 

Imaging of the metastasis to this patient’s L4 vertebra demonstrated spinal cord compression and L4-L5 right neural foraminal stenosis. Prior to the procedure, this caused severe local and radicular pain uncontrollable with narcotic medication. After the procedure, not only was the patient’s pain controlled, but subsequent imaging showed a reduction in the size of the tumor with improvement in the spinal canal and foraminal stenosis. 

Earlier methods of RFA were less consistent in producing a predictable ablation volume.³ The SpineSTAR Ablation Instrument mitigates this shortcoming with unipedicular access, an articulating probe, and accurate temperature measurement sensors. Furthermore, the operator is able to apply bone cement during the RFA procedure, which can be especially helpful in preventing fractures due to large vertebral body metastases with large post ablation necrosis cavities.⁴ 

Conclusion

The STAR device allows for a minimally invasive, single-access procedure that provides significant pain relief in vertebral metastases where traditional palliation methods fall short. Currently, there are few reported ASPS cases involving the vertebrae in the literature and limited data with respect to long term outcomes of ASPS patients treated with RFA; therefore, the need for further studies is critical.

Editor’s note: Disclosure: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest Dr. Howard reports unpaid consultancy to DFINE, Inc. Mr. Hampton reports no related disclosures.

Address for correspondence: Clifford Howard Jr., MD, Wake Forest University Baptist Medical Center, Medical Center Boulevard, Winston Salem, NC 27157. Email: clhoward@wakehealth.edu

Suggested citation: Howard C Jr., Hampton DG. Radiofrequency ablation of vertebral alveolar soft part sarcoma metastasis with the star tumor ablation system after attempted palliation with external beam radiation. Intervent Oncol 360. 2015;3(2):E18-E23.

References

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4. Proschek D, Kurth A, Proschek P, Vogl TJ, Mack MG. Prospective pilot-study of combined bipolar radiofrequency ablation and application of bone cement in bone metastases. Anticancer Res. 2009;29(7):2787-2792.