Primary Anorectal Melanoma
In April 2013, a 71-year-old female with no significant past medical history presented to our institution with painful bowel movements for the last 3 months. The patient also noticed blood-streaked stools and reported a 16-lb unintentional weight loss over a 1-year period. The review of her systems was negative otherwise. On examination: the woman was 5′ 7.5′ (1.715 m) tall, weight was 172 lb (78.019 kg), with a BMI of 26.54, and her vital signs were normal. Digital examination of the rectum revealed two small hemorrhoids at the 6 o'clock position and a firm, nonobstructing mass near the anal verge. The patient underwent a colonoscopy in September 2013 which revealed a nonobstructing, ulcerated anal mass, approximately 1 cm from the anal verge. A biopsy of the mass demonstrated an invasive, poorly differentiated carcinoma (fig. ). Stains for CK5/6 and P63 were positive, likely suggesting a primary squamous cell carcinoma of the anus. Tumor markers including CEA, CA 15–3 and CA 27–29 were negative. A CT of the abdomen and pelvis demonstrated an abnormal mass at the anorectal junction, with no evidence of lymph nodes or liver metastases in September 2013 (fig. ). PET combined with a CT scan demonstrated marked metabolic activity in the primary anal mass and a 1-cm perirectal lymph node near the coccyx, suggesting a node-positive disease in October 2013 (fig. ). An MRI of the pelvis confirmed the PET/CT findings (fig. ). The patient's tumor was sent to an outside institution for a second opinion, and the report was concluded as the tumor may in fact be a malignant melanoma. The patient subsequently underwent an exploratory laparotomy with an APR and left-end colostomy in October 2013. The patient tolerated the surgical procedure without any complications. The pathologic specimen confirmed a malignant melanoma arising in the anal skin and extending into the rectum, involving the anal and perirectal soft tissue and 6 regional lymph nodes (fig. ). The tumor was classified as grade 3, poorly differentiated, stage IIIA, T2N1M0 according to the tumor-node-metastasis classification of colorectal cancer []. Immunohistochemical analysis results were positive for the expression of the S-100 protein, HMB-45 and vimentin, whereas negative for the expression of cytokeratin and SMA (fig. ). The patient agreed to the plan of starting chemotherapy with mitomycin and 5-fluorouracil (for the anorectal melanoma).