Primary Gastric Melanoma with Rhabdoid Features: A Case Report
A 59-year-old male presented with a gastric mass that was found incidentally on gastroesophagoscopy. The only relevant history was a recent cerebral hemorrhage that occurred three months prior. Endoscopically, the mass was polypoid in appearance at the posterior wall of the fundus (). Stomach computed tomography showed an enhancing mass measuring 4.0 cm in diameter with central necrotic change at the cardia, and one enlarged regional lymph node, measuring 1.0 cm in diameter, posterior to the cardia. Under the impression of gastric carcinoma, total gastrectomy was performed. Preoperative endoscopic biopsy was not undertaken. A fungating grayish-tan colored mass was found at the posterior wall of the cardia, involving the esophagogastric junction. The cut surface of the polypoid mass revealed a homogeneous grayish-tan in appearance with focal hemorrhagic changes and focal mucosal ulcer. The mass invaded mucosa, submucosa, and inner proper muscle. It extended to the esophagogastric junction. Histologically, a solid growth pattern and pseudoalveolar clefts were found (). The mass was infiltrated by round, small-to-large-sized cells with plump eosinophilic cytoplasm and peripherally compressed nuclei, creating an occasional rhabdoid appearance. The tumor cells had an irregular shape with angulated nuclei, irregular nuclear contours, and fine chromatin. Occasional marked pleomorphic cells were found. Mitotic figures were counted up to 15/10 high power fields. Metastatic foci were demonstrated in one of 20 regional lymph nodes. The observed normal-appearing gastric and esophageal mucosa showed no abnormalities. Under the impression of malignant melanoma, gastrointestinal stromal tumor, poorly differentiated rhabdomyosarcoma, myeloid sarcoma, lymphoma, or plasmacytoma, immunohistochemistry and electron microscopic examination was performed. The tumor cells, both rhabdoid and nonrhabdoid, were diffusely positive for vimentin (prediluted, V9, Dako, Glostrup, Denmark) and S-100 protein (prediluted, polyclonal, Dako) (). They showed focal nuclear positivity for Sox 10 (prediluted, goat polyclonal, Santa Cruz Biotechnology Inc., Santa Cruz, CA, USA) (). They were negative for human melanoma black-45 antigen (HMB-45 antigen, prediluted, Dako), Melan-A (prediluted, A103, Dako), CD117 (prediluted, c-kit, Dako), CD34 (prediluted, QBEnd10, Dako), calretinin (1:100, calret 1, Dako), pancytokeratin (prediluted, AE1/AE3, Dako), epithelial membrane antigen (prediluted, E29, Dako), myoD-1 (1:50, 5.8A, Dako), myogenin (1:50, MyG007, Biocare Medical, Concord, CA, USA), smooth muscle actin (prediluted, IA4, Dako), desmin (prediluted, D33, Dako), synaptophysin (prediluted, SY38, Dako), chromogranin (prediluted, DAK-A3, Dako), CD56 (1:100, 123C2, Dako), CD68 (1:50, PG-M1, Dako), leukocyte common antigen (prediluted, Dako), CD79a (1:50, JCB117, Dako), CD138 (prediluted, MI/5, Dako), and CD99 (prediluted, 12E7, Dako). Staining with Fontana-Masson technique highlighted dark, black-colored cytoplasmic granular pigments within the tumor cells just beneath the ulcer (), although some of those melanin pigments were identified on hematoxylin and eosin staining. The cells showed negative results for Prussian blue, periodic acid-Schiff, myeloperoxidase, toluidine blue, lysozyme, and terminal deoxynucleotidyl transferase tests. Ultrastructurally, closely-apposed oval-shaped tumor cells displayed a moderate amount of cytoplasm containing mitochondria and secondary lysosomes. Extensive repeated ultrastructural evaluation revealed a few stage-3 melanosomes (). Some tumor cells had focal paranuclear accumulation of intermediate filaments with entrapped organelles (). No demonstrable cell junctions were observed. All of these findings were consistent with malignant melanoma with rhabdoid features. The patient was re-evaluated. Upon careful physical examination of his entire body surface, including oral and anal mucosa, no lesions were found, and fundoscopic examination of the eye was also normal. He was diagnosed as a presumptive primary malignant melanoma with a rhabdoid phenotype, although no demonstrable intraepithelial melanocytosis or in situ lesion was observed. Three months later, the patient developed low back pain; spine magnetic resonance imaging with enhancement study showed a compression fracture at L3 and a small bone marrow lesion at S5, suggesting a metastatic spinal tumor at L3 and S5, which was confirmed to be meta static melanoma by percutaneous needle biopsy. Vertebroplasty was performed, and during the four months following the operation, palliative chemoradiotherapy with dacarbazine was administered.