Signet-ring cell melanoma of the gastroesophageal junction: a case report and literature review.

We report the first case, to our knowledge, of a possible primary, signet-ring cell melanoma of the gastroesophageal junction. The mass was initially diagnosed as an invasive, poorly differentiated carcinoma; however, on further review and immunohistochemical workup, the diagnosis of signet-ring cell melanoma was made. The lesion consisted of oval to round epithelioid cells undermining the gastric mucosa and infiltrating the muscularis mucosae. Tumor cells demonstrated abundant cytoplasm and eccentrically located nuclei, many with signet-ring cell morphology. The tumor cells were negative for mucin and pancytokeratin, strongly positive for S100 protein and Melan-A, and focally but strongly positive for human melanoma black-45. Diagnostic imaging failed to prove another site of melanoma, and no history of melanoma or cutaneous lesion was reported by the patient. Therefore, it was determined this was likely a primary lesion. We review the literature and previously reported cases of this rare histologic variant of melanoma.