Patterns of Care and Survival Outcomes in the Treatment of Anal Melanoma

An uncommon case of anorectal malignant melanoma (ARMM): Clinical presentation and surgical outcome

INTRODUCTION AND IMPORTANCE

Anorectal mucosal melanoma (ARMM) is a rare disease with a poor prognosis. However, surgery is often difficult, due to the lentiginous growth pattern of such melanoma.

CASE PRESENTATION

A 61 years old lady presented with anal pain for 1 year, associated with painless fresh per rectal bleeding post defecation and altered bowel habit. Physical examination showed hyperpigmentation at the anal verge, extending to the dentate line. CT, MRI and PET imaging showed localised disease. She underwent pelvic exanteration and radical lymph node dissection with gracilis flap coverage. Post operatively, she recovers well, and was discharged well on day 8. HPE came back as malignant melanoma, with 1 out 12 lymph nodes involved. She was subsequently referred to oncology, started on pembrolizumab immunotherapy.

CLINICAL DISCUSSION

Anorectal melanoma is an aggressive disease, often present with delayed diagnosis. Multiple imaging has been proposed, however none is standardized to diagnose ARMM. Immunohistochemical stains such as S-100 protein, MelanA and tyrosinase and with HMB-45 help in diagnosis and are sensitive for melanocytic differentiation. Surgery excision remains the most common and superior initial treatment for ARMM. One retrospective study done to compare different treatment modalities has shown that patients with surgical excision and radiation therapy had the highest median survival at 32.3 months but surgical excision remains the single best modality for ARMM.

CONCLUSION

Suspicious hyperpigmentation at the anal region should raise clinical awareness. Surgical excision with optimal margin is indicated to achieve favourable symptom control, reduce local recurrence and improve survival rate.

[Anorectal melanoma : Update on clinical presentation, diagnosis and treatment]

Anorectal melanomas are a rare malignant type of cancer and pose a diagnostic challenge due to their hidden anatomical location. They are associated with nonspecific clinical symptoms and are therefore often misinterpreted as benign disease. The result is delayed diagnosis in the locally advanced or metastasized stage and an unfavorable prognosis. Given the overall low incidence of the tumor, no consensus guidelines for diagnosis or therapy are established either internationally or nationally at present. The present work intends to provide a comprehensive overview of the clinical aspects, diagnostics, and therapeutic approaches of anorectal melanoma based on the currently available literature.

Anorectal melanoma

Anorectal melanoma is an aggressive mucosal melanoma subtype with a poor prognosis. Although recent advancements have been seen for cutaneous melanoma, the optimal treatment paradigm for management of anorectal melanoma is evolving. In this review, we highlight differences in the pathogenesis of mucosal versus cutaneous melanoma, new concepts of staging for mucosal melanoma, updates to surgical management of anorectal melanoma, and current data for adjuvant radiation and systemic therapy in this unique patient population.

Impact of adjuvant therapies following surgery for anal melanoma

BACKGROUND

Anal melanoma is rare. Surgery is standard of care for non-metastatic disease. There are limited data supporting adjuvant therapy. We sought to examine the impact of adjuvant radiation, chemotherapy and immunotherapy on survival.

METHODS

The National Cancer Database was queried. Factors associated with overall survival were examined by Kaplan-Meier and Cox proportional hazards analyses. Patients were grouped by treatment regimen.

RESULTS

450 patients had complete treatment data: surgery alone (63.8%), surgery + radiation (14.9%), surgery + chemotherapy (7.6%), surgery + immunotherapy (9.6%) and non-surgical treatment (4.2%). Median survival was 27.2 months. Node-positive patients had worse survival than node-negative (22.4 vs. 36.8 months; p = 0.0002). Non-surgical treatment yielded worse survival than any surgery-inclusive regimen (10.4 vs. 27.8 months; p = 0.0002). No adjuvant modality conferred a survival advantage. By multivariate analysis, increasing age (HR/1 year = 1.02, p = 0.012) and node positivity (HR = 2.10, p = 0.0002) negatively impacted survival.

CONCLUSION

Adjuvant therapy for non-metastatic anal melanoma does not appear to influence survival.

Surgical treatment of anorectal melanoma: a systematic review and meta-analysis

Background

Anorectal melanoma is a rare neoplasm with a poor prognosis. The surgical approaches for anorectal melanoma can be categorized into local excision (procedures without lymph node removal and preservation of the rectum) and extensive resection (procedures with rectum and pararectal lymph node removal). The aim of this systematic review and meta-analysis was to compare the survival of patients who underwent extensive resection with that of patients who underwent local excision, stratifying patients according to tumour stage.

Methods

A literature review was performed according to PRISMA guidelines by searching MEDLINE/PubMed for manuscripts published until March 2021. Studies comparing survival outcomes in patients with anorectal melanoma who underwent local excision versus extensive resection were screened for eligibility. Meta-analysis was performed for overall survival after the different surgical approaches, stratified by tumour stage.

Results

There were 347 studiesidentified of which 34 were included for meta-analysis with a total of 1858 patients. There was no significant difference in overall survival between the surgical approaches in patients per stage (stage I odds ratio 1.30 (95 per cent c.i. 0.62 to 2.72, P = 0.49); stage II odds ratio 1.61 (95 per cent c.i. 0.62 to 4.18, P = 0.33); stage I–III odds ratio 1.19 (95 per cent c.i. 0.83 to 1.70, P = 0.35). Subgroup analyses were conducted for the time intervals (<2000, 2001–2010 and 2011–2021) and for continent of study origin. Subgroup analysis for time interval and continent of origin also showed no statistically significant differences in overall survival.

Conclusion

No significant survival benefit exists for patients with anorectal melanoma treated with local excision or extensive resection, independent of tumour stage.