S2965 Melanoma Presenting as Upper Gastrointestinal Bleed: Rare Primary vs Metastasis of Unknown Origin

Abstract

INTRODUCTION: Melanoma is the most serious form of skin cancer and the fifth most common cancer in the United States. It generally appears where melanocytes are found in abundance including the eyes, skin and anal region. When found in the GI tract, the overwhelming cause is metastatic spread. This manifests as abdominal pain, fatigue, GI bleeds and their sequelae. Primary gastric melanoma is an exceedingly rare entity requiring thorough physical examination and imaging in order to rule out metastatic disease as the cause. We present a case of GI bleed secondary to gastric melanoma in which no other primary lesion was noted. CASE DESCRIPTION/METHODS: A 92-year-old man with a history of non-melanotic skin cancer presented to the emergency department with a 3-day history of melena. He was found to be hemodynamically stable with a mild normocytic anemia. He had never had an EGD and most recent colonoscopy was 15 years prior, notable for only diverticulosis. EGD performed during admission was significant for a large cratered mass in the gastric body identified as the source of bleeding. Biopsies were taken of the mass and returned strongly positive for S-100, Melan-A and Sox-10, consistent with malignant melanoma. Further evaluation with dermatology as well as oncology involved a thorough physical exam with skin check, PET CT as well as MRI brain, none of which revealed any other primary lesion consistent with melanoma. Due to the patient’s age, a decision was made to treat non-surgically. He opted for single-agent immunotherapy with pembrolizumab. PET CT after four cycles showed that the lone site of uptake in the stomach was no longer hypermetabolic. Patient has since finished eight cycles of pembrolizumab. DISCUSSION: This is a case of gastric melanoma in which no primary oculocutaneous source was identified. Given the exceedingly rare incidence of primary gastric melanoma, cases like these raise the question of a regressed primary cutaneous melanoma. This case illustrates that when GI melanoma is identified, a thorough skin exam and PET imaging are warranted to rule out a more common primary source. However, a negative evaluation does not completely eliminate the possibility of metastasis from a more common origin.Figure 1.: Gastric Melanoma Prior to Biopsy.