Breast tumors with a solid and uniform carcinoid pattern. Ultrastructural and immunohistochemical study of two cases.

Two cases of breast tumors with a uniform solid carcinoid pattern and argyrophilic dense-core granules were analyzed by immunohistochemistry in order to compare their characteristics with known features of other carcinoid tumors and ordinary breast carcinomas. The tumors were positive for keratin-type intermediate filaments, neuron-specific enolase and alpha-chain of human chorion gonadotropin but negative for vimentin and S-100 protein. Laminin was found only in a rim between tumor cell islands and stroma but not among the cells. It is concluded that these tumors are histologically, ultrastructurally and immunohistochemically similar to other carcinoid tumors. The present results suggest that both breast carcinoids and carcinomas may have a common precursor in the mammary secretory unit.