AbstractWe report on a case of invasive lobular carcinoma of the breast with a previously undescribed cytologic feature. Diff‐Quik‐stained cytologic preparations showed uniform single cells with prominent coarse cytoplasmic granules. Ultrastructurally, the granules showed features suggestive of autophagosomes and/or degenerative mitochondria. The cytologic differential diagnosis included granulocytic sarcoma, metastatic melanoma, extramedullary hematopoiesis, large granulocytic leukemia/lymphoma, and mast‐cell tumor. Adjunctive studies were helpful in the diagnosis of carcinoma. Histologic study of the mastectomy specimen showed classic type of invasive lobular carcinoma. Diagn. Cytopathol. 25:253–257, 2001. © 2001 Wiley‐Liss, Inc.