A 92 year old woman underwent an ultrasound guided biopsy for a mass in the 4:00 position of the right breast.
Diagnosis: Invasive mammary carcinoma with adenoid cystic features.
Discussion: The dual cell population, pattern of infiltration, and low grade are characteristic of adenoid cystic carcinoma (ACC). Individual cellular nests of ACC usually contain both cell types, with the formation of true and false lumens, the latter created by collections of basement membrane material. This case is unusual in that the dual cell population seems to be restricted to individual nests, with luminal cells in some nests, and myoepithelial cells containing basement membrane material in other nests. Not surprising, this low grade carcinoma was negative for expression of estrogen and progesterone receptors, as well as HER2.