Should Abdominoperineal Excision Be Considered as the Initial Treatment for a Primary Anorectal Malignant Melanoma?

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An anorectal melanoma is a rare tumor with poor survival. The clinical diagnosis of an anorectal melanoma is difficult because of its nonspecific symptoms and the lack of pigmentation in a significant proportion of lesions (37% in this report). To my knowledge, this is the largest clinical series studying anorectal melanomas in Korea even though the number of cases (19 cases) is small.

Although the majority of patients die of systemic metastasis, the role of adjuvant chemotherapy and immunotherapy in the treatment of an anorectal melanoma is minimal. The major debate is the extent of surgery (wide local excision versus radical resection). Within the limitation of a small number of cases and a short follow up, this study suggests that the abdominoperineal resection (APR) may provide a longer survival, compared with the wide local excision, in cases involving an anorectal melanoma.

In a retrospective study at the Memorial Sloan-Kettering Cancer Center, Yeh et al. [1] reported a change in practice patterns during 20 years. In their study of 46 patients with an anorectal melanoma, the authors noted a paradigm shift in the treatment strategy from APR to local excision (LE). They reported that, between 1984 and 1996, 15 of 21 (71%) patients treated for primary an anorectal melanoma underwent an APR. From 1997 to 2003, however, 21 of 25 (84%) patients treated for an anorectal melanoma underwent a LE. During these respective periods, no changes were seen in the thicknesses and the diameters of the tumors. In addition, the pattern of relapse, the time to relapse, and the disease-specific mortality remained similar in these two cohorts. Despite the clear change in practice patterns during these two periods, the outcomes were not significantly different, regardless of the extent of resection. The five-year disease-specific survival for the entire cohort was 34%, with a median follow-up of 39 months for survivors. Thirty-four (74%) of 46 patients relapsed, with a median relapse-free survival of 10 months and an overall recurrence rate of 53% at 1 year. The majority of patients developed distant recurrences. No differences were seen in patterns of relapse between patients treated with an APR or a LE: 5 of 19 (26%) patients in the APR group and 7 of 27 (26%) in the LE group developed local recurrence as the first site of relapse. Survival was similar in both groups, with 5-year disease-specific survivals of 32% for the APR group and 35% for the LE group. These findings suggest that local recurrence and survival in patients with an anorectal melanoma are not associated with the extent of resection.

A systematic review that included 14 series also showed no stage-specific survival advantage for the APR [2]. Recently Nilsson and Ragnarsson-Olding [3] reported that there was no statistically significant difference in terms of median survival (11 months vs. 14 months) or the five-year survival rate (7% vs. 15%) between patients treated with the APR or the LE (P = 0.084). When 72 patients in whom a R0 resection had been achieved were compared with patients having involved margins (R+), there was a significant difference in survival in favor of the R0 resection; thus, both the APR and the LE seemed appropriate for treating an anorectal melanoma, provided clear margins could be achieved. Because of the APR having no survival advantage over the LE and because of the poor prognosis associated with an anorectal melanoma, further consideration must be given to quality-of-life issues when making treatment decisions between these two treatment options.