Eosinophilic and granular cell tumors of the breast.

Eosinophilic and granular cell tumors of the breast are a heterogeneous group encompassing both epithelial and mesenchymal lesions. A granular appearance of the cytoplasm may be caused by the accumulation of secretory granules, mitochondria, or lysosomes. In the breast, mucoid carcinomas, carcinomas showing apocrine differentiation, and neuroendocrine carcinomas are well known entities, while tumors with oncocytic and acinic cell differentiation have been only recently recognized. An abundance of lysosomes is characteristic of Schwannian granular cell neoplasms, but smooth muscle cell tumors also may have this cytoplasmic feature. Awareness of all these possibilities when granular cells are found in breast lesions improves diagnostic accuracy and helps to avoid misdiagnosis of both benign lesions and malignant tumors.