1568 Don't Skip the Retroflexion: A Case of Disseminated Anorectal Mucosal Melanoma

Abstract

INTRODUCTION: Less than 4% of melanomas are of mucosal origin with primary anorectal mucosal melanomas comprising a small subset. Mucosal melanomas are often diagnosed late due to delay in patient presentation and obscured tumor origins noting a more aggressive behavior and less favorable prognosis when compared to cutaneous melanomas. We present a case of metastatic anorectal mucosal melanoma with a negative colonoscopy 1-year prior. CASE DESCRIPTION/METHODS: A 68 year-old female presented to the hospital with a history of several months of intermittent fecal impaction complicated by sporadic outlet type rectal bleeding and a negative colonoscopy 1-year prior. She endorsed progressive anorexia and a 20 lb. weight loss over the last few months. She was hemodynamically stable with normal hemoglobin level. CT imaging depicted multiple lesions in the liver and lungs concerning for metastatic disease. A colonoscopy was repeated and revealed a rigid mass on rectal exam and granular nodularity with ulceration in the rectum at the dentate line on retroflexion (Figure 1). Excisional biopsy confirmed mucosal melanoma. Same session endoscopic ultrasound showed several lesions in the left lobe of the liver with FNA demonstrating malignant melanoma (Figures 2 and 3). MRI revealed primary tumor involvement of the anal canal and rectum in addition to metastases to the liver, lungs, and lymph nodes. The patient was diagnosed with T4N1M1, stage IV anorectal mucosal melanoma (BRAF/C-KIT negative) and was recommended to undergo ipilimumab and nivolumab (I3/N1) immunotherapy with palliative radiation. DISCUSSION: Anorectal mucosal melanomas occur infrequently, but at the time of diagnosis, are more likely to be metastatic with poor prognoses. Rectal bleeding is the most common symptom, and diagnosis is often seen in fifth to seventh decade of life. This case is a prime example of not only the aggressive nature of anorectal mucosal melanoma presenting with disseminated disease despite normal colonoscopy 1-year prior but also of the significance of the rectal exam and retroflexion maneuver during colonoscopy.