Following right breast mastectomy and sentinel lymph node biopsy, final pathology revealed a biphasic neoplasm composed of both ACC and lobular carcinoma (LC) components. The ACC component exhibited classic cribriform and tubular architecture, a triple-negative immunophenotype, strong transformation-related protein 63 (p63) and cluster of differentiation 117 (CD117; c-Kit) positivity, and a low Ki-67 proliferation index (9.8%). This evidence concerns the gene MKI67 and breast lobular carcinoma.