Metastatic Gastric Mucosal Melanoma: A Rare Case Presenting With Diffuse Gastric Polyposis

We report a 66-year-old Chinese lady who presented with a three-month history of postprandial vomiting, early satiety, anorexia and weight loss, and significant physical findings of hepatomegaly and ascites. Gastroscopy revealed gastric polyposis with both hyperpigmented and unpigmented lesions over the gastric fundus, body, and proximal antrum, biopsies of which yielded malignant melanoma histologically. Cross-sectional imaging with CT also demonstrated extensive hepatic and bony metastases. No cutaneous or ocular primary was detected. She was treated with a combination of ipilimumab and nivolumab but developed interval progression of hepatic metastases after two cycles of immunotherapy. The patient eventually succumbed two months after diagnosis.