The pigmented "black" neuroendocrine tumor of the pancreas: a question of origin.
BACKGROUND: Pigmented neoplasms are extremely rare in the pancreas, and, when black pigment is identified, it often suggests the diagnosis of metastatic melanoma. The authors describe two patients with pigmented "black" neuroendocrine tumors of the pancreas. One patient had an incidental (0.5 cm) finding, and the second patient had a well-demarcated, 4.5-cm mass identified by computerized tomography that was consistent with an islet cell tumor. METHODS: The two neoplasms were resected surgically and studied by light microscopy using hematoxylin and eosin (H&E), Fontana-Masson, and iron stains. The neoplasms were examined immunohistochemically, and ultrastructural analysis was performed. RESULTS: H&E stains revealed nests of well-differentiated cells with small, round, centrally placed nuclei. The cytoplasm of the neoplastic cells was pink and granular and contained abundant brown-black pigment. Angiolymphatic and perineural invasion were identified in the larger neoplasm. Both neoplasms demonstrated a positive reaction with a Fontana-Masson stain, which was susceptible to bleaching, and a negative reaction to an iron stain. Immunohistochemical stains showed that neoplastic cells expressed chromogranin and synaptophysin but did not express HMB-45, S-100 protein, glucagon, or insulin. Ultrastructural examination revealed regular neurosecretory granules (100-150 nm) and large, irregularly shaped, electron-dense granules with small lipid inclusions consistent with lipofuscin. CONCLUSIONS: These pigmented pancreatic neoplasms are similar histologically and radiographically to the "black adenoma" of the adrenal gland. It is important to recognize these tumors, because they may mimic metastatic melanoma.