Expression of c-kit in adenoid cystic carcinoma of the breast.

Breast adenoid cystic carcinoma (BACC) is a biologically distinct tumor with morphologic mimickers, which might make accurate classification problematic. Because c-kit expression has been reported in adenoid cystic carcinoma of various anatomic sites, we evaluated BACC for c-kit by immunohistochemical analysis, comparing the findings to similarly stained mimickers. Tested cases included 6 BACCs, 15 low-grade infiltrating ductal carcinomas (LGIDCs) chosen as potential mimickers, and 15 head-neck adenoid cystic carcinomas (HNACCs). All BACCs showed plasma membranous and cytoplasmic staining equal to or greater than that of adjacent benign epithelium. Five BACCs (83%) expressed c-kit in more than 50% of tumor cells. Only 2 of 15 LGIDCs expressed low-intensity, focal c-kit staining. Of the 15 HNACCs, 10 (67%) expressed c-kit. Hormone receptors were consistently negative in BACCs. All BACCs expressed c-kit, whereas LGIDCs infrequently expressed low-intensity c-kit. Immunohistochemical evaluation for c-kit might aid in accurately classifying carcinomas with histologic features overlapping adenoid cystic carcinoma and LGIDC.