A 64-year-old man presented with multiple metastatic malignant masses throughout the body. (Fig. 1A and 1B). Endoscopic examination revealed umbilicated nodules of various sizes in the stomach (Fig. 1C) and a nodule with peripheral pigmentation in the rectum (Fig. 1D). Malignant melanoma was diagnosed in all endoscopic forceps biopsies (Fig. 1E and 1F). He was diagnosed with malignant melanoma with multiple metastases and an unclear primary site. Nivolumab treatment (human programmed death receptor-1 [PD-1] blocking antibody) was started at 3 mg/kg every 2 weeks. Most metastases and endoscopic malignant nodules disappeared after 6 months of treatment (Fig. 2).