Simultaneous endocrine expression and loss of melanoma markers in malignant melanoma metastases, a retrospective analysis.

Malignant melanoma metastases are chameleons of histopathology. In 4 primary malignant melanomas and 20 melanoma metastases expression of S-100, HMB-45 and melan-A as melanoma markers and CD56, synaptophysin and chromogranin-A as neuroendocrine markers was retrospectively analyzed. While all primary tumors expressed all 3 melanoma markers 7/20 of melanoma metastases had lost at least one melanoma marker, one had lost all three markers. Conversely about half of the samples stained for CD56, only 6/20 metastases were negative for all 3 neuroendocrine markers. None expressed chromogranin-A. Partial loss of melanoma markers and expression of neuroendocrine markers seems not to be infrequent. In patients with a history of malignant melanoma and suspected metastases, losing melanoma markers while expressing neuroendocrine markers is a potential diagnostic pitfall. Therefore all 3 melanoma markers should be performed as well as chromogranin-A staining. In doubt, metastases of the melanoma should be assumed.