Role of Endoscopy and PET Imaging in Anorectal Melanoma: A Call for More Aggressive Diagnostic and Follow-up Strategy for Mucosal Melanomas

Abstract

Purpose: A 63-year-old man presented to his primary care physician with pelvic pain and blood in stool in October, 2008. He underwent esophagogastroduodenoscopy (EGD) which was reportedly normal, and colonoscopy which showed hemorrhoids and two small tubular adenomas (TA). Due to continued rectal bleeding, he was referred to us for further management. Repeat colonoscopy revealed multiple small TA polyps, and a large 4x4-cm distal rectal polypoid mass above the dentate line. Pathology of rectal mass revealed small superficial fragments of tubulovillous adenoma (TVA) and a separate fragment of ulcerated and focally necrotic epithelioid neoplasm, with cells arranged in sheets, columns and rosettes and containing melanin appearing pigment. The specimen was moderately positive for S-100 but strongly positive for Melan A (melanin). EUS was also performed to assess depth of invasion of melanoma, and it was confined to submucosa. Patient chose chemoradiotherapy with fluorouracil and temozolamide followed by abdomino-perineal resection of rectal mass in November, 2009. The tumor demonstrated extensive infiltration of the muscle wall of the rectum with tumor deposits in perirectal soft tissue. Intramucosal adenocarcinoma arising in TVA was seen. Invasive melanoma was confined to the polyp (lamina propria). 11/36 lymph nodes positive for melanoma. He was started on the sorafenib and continued to have surveillance CT and PET scans. In 9/2012 he underwent EGD for evaluation of thickened gastric folds seen on surveillance CT, which showed 2 pigmented nodules in gastral body. Biopsy confirmed melanoma with immunophenotype similar to rectal mass. Chemotherapy with sorafenib was continued. EGD was repeated 5/2013 which showed one new lesion along with increasing size of 2 previous gastral melanomas despite being on the chemotherapy. Primary mucosal melanomas account for 1.4% of total melanomas in the U.S. The most common sites of primary GI melanomas are anorectal (31.4% anal canal and 22.2% rectum) and oropharyngeal region (32.8%), followed by esophagus (5.9%), stomach (2.7%), small bowel (2.3%), gallbladder (1.4%), and colon (0.9%). Besides the rarity of finding an already rare mucosal melanoma co-existing with adenocarcinoma within a TVA, our case emphasizes on some important clinical issues in management of mucosal melanomas. While cutaneous melanoma management is a well described science with most follow-up largely radiology based, there are no concrete guidelines for mucosal melanomas. It is plausible that synchronous mucosal melanomas occurred in rectum and stomach earlier than diagnosed and were missed by CT/PET imaging, which urges for endoscopic follow-up of mucosal melanomas, rather than solely imaging based.