The pigmented "black" neuroendocrine tumor of the pancreas - A question oforigin

BACKGROUND. Pigmented neoplasms are extremely rare in the pancreas, and, wh en black pigment is identified, it often suggests the diagnosis of metastat ic melanoma. The authors describe two patients with pigmented "black" neuro endocrine tumors of the pancreas. One patient had an incidental (0.5 cm) fi nding, 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 mi croscopy using hematoxylin and eosin (H&E), Fontana-Masson, and iron stains . The neoplasms were examined immunohistochemically, and ultrastructural an alysis 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. Angiolymphati c and perineural invasion were identified in the larger neoplasm. Both neop lasms demonstrated a positive reaction with a Fontana-Masson stain, which w as susceptible to bleaching, and a negative reaction to an iron stain. Immu nohistochemical stains showed that neoplastic cells expressed chromogranin and synaptophysin but did not express HMB-45, S-100 protein, glucagon, or i nsulin. Ultrastructural examination revealed regular neurosecretory granule s (100-150 nm) and large, irregularly shaped, electron-dense granules with small lipid inclusions consistent with lipofuscin. CONCLUSIONS. These pigmented pancreatic neoplasms are similar histologicall y and radiographically to the "black adenoma" of the adrenal gland. It is i mportant to recognize these tumors, because they may mimic metastatic melan oma. (C) 2001 American Cancer Society.