Mucosal melanomas of the anorectum are extremely rare, and therefore standards of care are not well established because large single- or multi-institutional experiences are lacking. The management strategies are designed based on the stage at presentation, the predicted sites of recurrence, and the combining of principles learned from treating cutaneous melanoma with surgical techniques used for the more common histologic solid malignancies of the anus and rectum, while at the same time minimizing long-term morbidity. As in this patient, most present with clinically localized disease, but have a very high rate of regional lymph node failure and the development of distant disease and death, despite initial surgery with curative intent. No current data demonstrate that abdominoperineal resection (APR) improves survival or regional control compared with local excision with negative margins. Therefore, contemporary surgical approaches include sphincter-sparing resections, if technically feasible, and a selective approach to the regional nodes using lymphatic mapping and SNB. Adjuvant regional and systemic therapies are often recommended because of the potential for local recurrence and the high rate of systemic failure.

A careful digital and proctoscopic examination by the operating surgeon is critical to assess the local extent of disease and determine if a local excision is feasible. The digital examination can detect submucosal extent of disease and satellite nodules that will not be visible. Furthermore, a thorough digital evaluation may detect perirectal nodal enlargement as well as presacral adenopathy. Finally, endorectal ultrasound is a good adjunct in evaluating perirectal extent of disease, particularly in patients with pure rectal mucosal lesions. The proctoscopy not only identifies the exact location of the primary tumor, but also the presence of multifocal mucosal disease.

Preoperative lymphoscintigraphy can be accomplished accurately by peritumoral mucosal injections of radiolabeled colloids to assess if unilateral or bilateral inguinal drainage exists or if the primary regional drainage is directly to the rectal mesenteric nodes. On the morning of surgery, the injection is repeated to facilitate performing the SNB in the same operative setting as the formal excision. The transanal resection is performed with the patient in either the lithotomy or prone position, depending on the location of the tumor. The SNB can be performed before or after the excision of the primary, and therefore one position change is required if the primary tumor resection is facilitated by the prone position. It should be cautioned that peritumoral blue dye injections for SNBs might obscure the surgeon’s ability to determine the mucosal extent of the tumor. Patients with positive sentinel nodes are offered completion node dissections.