Anal versus rectal melanoma: does site of origin predict outcome?

BACKGROUND

Anatomic site is a predictive factor in subtypes of cutaneous and mucosal melanoma.

OBJECTIVE

The aim of this study was to examine the clinical relevance of location of origin of anorectal melanoma as a prognostic factor.

DESIGN

With the use of a prospectively maintained database, clinical characteristics, management, and outcomes were compared according to the site of origin. SETTINGS, PATIENTS, INTERVENTIONS: A retrospective review was conducted of patients diagnosed with anorectal melanoma from 1994 to 2010. Tumors were defined as anal, anorectal, or rectal melanoma according to their anatomic relationship to the dentate line.

MAIN OUTCOME MEASURES

Clinicopathologic factors were compared by χ2 test. Time-to-event analysis was performed by Kaplan-Meier analysis.

RESULTS

Of the 96 patients included (41 with anal melanoma, 32 with anorectal melanoma, 23 with rectal melanoma), patients with rectal and anorectal mucosal melanoma had advanced primary tumors (median Breslow thickness, 12 mm and 8 mm, p = 0.002), whereas anal lesions could be found at earlier depths (median thickness, 6.5 mm). Patients with anal tumors more commonly underwent transanal excision (p < 0.02) and sentinel lymph node biopsy (p = 0.004) versus anorectal and rectal tumors. Patterns of recurrence were also distinct; nearly two-thirds of anorectal and rectal tumors recurred systemically, whereas anal melanoma more often recurred within the lymph nodes first (63%; p < 0.02). Recurrence occurred in 24 (59%) patients with anal tumors, 23 (72%) patients with anorectal tumors, and 16 (70%) patients with rectal tumors. Median overall survival was 22 months for anal melanoma, 28 months for anorectal melanoma, and 27 months for rectal melanoma. Recurrence and survival were not statistically different between the groups.

LIMITATIONS

This study is limited by small sample size and its retrospective nature.

CONCLUSIONS

This study represents the only series describing the outcomes of anorectal melanoma by anatomic location. Lesions at or proximal to the dentate line present with more advanced disease, possibly related to a delay in diagnosis. Lesions distal to the dentate line more commonly recur within lymph nodes, which may represent differences in nodal drainage. Irrespective of location, the long-term prognosis remains poor for all cases of anorectal melanoma.