Metastatic Gastric Melanoma with an Unknown Primary Presenting as a GI Bleed

Abstract

Purpose: A 67-year-old male inmate presented with a 4 month history of dyspnea, weight loss, nausea, vomiting, and abdominal pain. He reported intermittent episodes of melena with profound anemia requiring blood transfusions. An endoscopy performed at an outside hospital showed possible metastatic lesions in the stomach that were biopsied. However, the pathology results were inconclusive because of insufficient tissue. He was sent to our facility for further evaluation. Patient had history of gastroesophageal reflux disease and arthritis. He denied tobacco or alcohol use. Family history was significant for prostate cancer. His physical examination was significant for mild epigastric tenderness. Initial laboratory data was significant for hemoglobin of 9.1g/dL and hematocrit of 28.6%. A complete metabolic panel was normal. CT scan revealed metastases in the right cardiac ventricle, bilateral adrenal, left gluteal mass and pancreatic tail. Diffuse mesenteric, celiac, external iliac and portal venous adenopathy was seen. Echocardiogram showed a mobile echodensity in the right ventricle. MRI of brain showed no masses. A repeat endoscopy revealed a large non-circumferential, non-pigmented, ulcerated gastric mass with stigmata of recent bleeding. The stomach biopsy showed sheets of loosely cohesive malignant polygonal cells consistent with malignant melanoma. HMB-45 and vimentin were positive. The patient denied any history of cancerous lesions of the skin. A complete examination of his skin, including oral and anal mucosa, showed no suspicious lesions, and fundoscopic examination of the eye was normal. He was diagnosed with metastatic gastric melanoma with an unknown primary. Unfortunately, patient refused further workup and returned to the correctional facility. Although more than 90% of melanomas have a cutaneous origin, occasionally it is discovered as a metastasis without evidence of a primary site. The incidence of metastatic malignant melanoma with an unknown primary (MUP) is 3.2 %. The frequently asymptomatic character of MUP explains why it often eludes detection. However, symptoms may include gastrointestinal bleeding, abdominal pain, nausea, and anorexia. Diagnosis requires careful inspection of the mucosa for metastatic lesions and biopsy with special immunohistochemical stains (HMB-45 and S100). This case is presented in view of its rare occurrence and the difficulties in its diagnostic course. Early detection and surgical intervention is critical for long term cure, though overall prognosis is poor.