The role of surgery in the treatment of anorectal melanoma

Background: Anorectal melanoma is a rare neoplasm. The diagnosis is almost always late and the prognosis is not favorable. Methods: The observation of a clinical case induced to a review of the literature of the last decade. Results: The annual incidence of this pathology is 1-2 cases/million (0.1-4.6% of all tumors of the anal canal ; 0.5-1.6% of all melanomas). Melanoma of the anorectum appear in most cases at the dentate line . The diagnosis is histologic. The immunohistochemistry is determinant (S100 protein, HMB-45,Melanin A and MITF). However the diagnosis is generally formulated in late phase and in 60% of cases the pathology is disseminated at the time of clinical encounter. The prognosis is generally bad. The median survival is 10 months for patients with distant metastases, 13 months for loco regional diffusion and 34 for patients with localized pathology. The 5-years survival is 10-20%. The thickness of the tumor is the most important prognostic factor; a melanoma with thickness > than 1 mm has a better prognosis. Surgery is the gold standard treatment for this kind of tumor because of the poor response to the radio and chemiotheraphy. The surgical intervention may be the local excision (LE) of the mass or an abdomino-perineal amputation (APR). Some studies demonstrate that the rates of local recurrence and disease-free survival at 5 years is equal for both interventions. A Study of Memorial Sloan Kettering (46 patients treated and followed for a period of 19 years) reported overlapping rates of local recurrence (26-21%) and disease-free survival at 5 years (35% -34%). Would seem to be no substantial differences between the two surgical options and the LE seems to be preferred. Conclusions: The thickness of the melanoma, a predictor for the risk of local and distant recurrence, can be used to plan the most suitable therapeutic procedure. For a neoplasm of thickness <1mm a LE with preservation of the sphincters and the free margin of 1cm may be considered sufficient, while for those with a thickness between 1 and 4mm requires a margin of at least 2cm (WLE). For tumors with a thickness greater than 4mm is necessary to use the APR with extended lymphadenectomy. We believe that we cannot ignore the correct staging of the tumor to analyze the degree of invasion of the intestinal wall and in accordance with Ischizone recommend an EL only in patients with melanoma at stage 0 and a APR extended lymph node dissection for those with stage 1 or invasion of the submucosa. In our patient the thickness of the neoplasia was > than 4mm with signs of invasion of the submucosa, and for this reason it was decided to perform an APR with extended lymph node dissection (lomboaortic, iliac and obturator lymph node stations), despite the negativity of intraoperative lymphoscintigraphy after labeling with radioactive marker of the primary tumor.