Primary gastric malignant melanoma might originate from amine precursor uptake and decarboxylation cells

Primary gastric malignant melanoma is a rare malignant tumor. The purpose of this study is to determine the origination of primary gastric malignant melanoma. We report a case of a 63-year-old male with a history of right limb movement disorder for one month. The patient underwent microscopic supratentorial mass resection and proximal stomach resection. Hematoxylin-eosin and immunohistochemical staining, amplification refractory mutation system analysis and transmission electron microscopy test were performed. Hematoxylin-eosin staining showed diffuse patchy distribution of tumor cells, the pleomorphism, epithelioid or fusiform, abundant cytoplasm, increased mitotic figures, and obvious melanin particles. Immunohistochemical results indicated positive expression for S-100, HMB45, Melan-A, CD56, NSE, Syn, CgA, Vimentin and bcl-2, and negative expression for CK-Pan, CD117, Dog-1, CD34, Desmin, Actin-ping, HHF35, MBP. BRAF V600E mutation was detected in primary gastric malignant melanoma. The neurosecretory granules were observed in the cytoplasm of melanoma cells. Pathological examination finally made a definite diagnosis of primary malignant melanoma, serosa layer and perigastric lymph nodes involved (1/20), with the left parietal lobe metastasis. Immunohistochemical and transmission electron microscopy test results indicated that primary gastric malignant melanoma might originate from amine precursor uptake and decarboxylation cells.