Invasive mammary carcinoma with neuroendocrine differentiation: a diagnostic challenge

Neuroendocrine differentiation has been reported in both in situ and infiltrating breast cancers. The prognostic significance of neuroendocrine differentiation in mammary carcinoma is unclear. The spectrum ranges from undifferentiated small cell carcinoma to ductal carcinoma in situ with neuroendocrine differentiation. Mucinous carcinomas of the breast appear to have the greatest association with neuroendocrine differentiation. We add to the literature a case of a morphologically composite mammary infiltrating ductal carcinoma with diffuse neuroendocrine differentiation as demonstrated by immunohistochemical staining. We reported a case of 76 year old female diagnosed as infiltrating ductal carcinoma in which there was a morphologically conventional-appearing infiltrating ductal component admixed with nests of cells that resembled a carcinoid tumor and initially mimicked the appearance of intraductal carcinoma. Immunohistochemical stains for synaptophysin and chromogranin demonstrated diffuse, strong positivity uniformly throughout the tumor, even in the more conventional-appearing areas. We concluded that this was an infiltrating ductal carcinoma with morphologic and immunohistochemical evidence of neuroendocrine differentiation. The presence of neuroendocrine differentiation in a morphologically composite tumor should be reported but that the tumor should essentially be classified according to existing schemes of ductal and lobular carcinomas and variants. There is no evidence that neuroendocrine differentiation is prognostically significant.