DIAGNOSIS: Adenoid cystic carcinoma in situ
Adenoid cystic carcinoma of the breast is a rare form of invasive carcinoma with an excellent prognosis. Characterized by a dual cell population, the invasive tumor nests contain true and false lumens. Using a Periodic Acid Schiff (PAS) stain, the true lumens contain neutral mucins, while the false lumens contain acidic mucins from basement membrane material. Adenoid cystic carcinoma occasionally is associated with microglandular adenosis, and the adenosis rarely contains an in situ component of adenoid cystic carcinoma.
The current case is unique in that all of the features characteristic of adenoid cystic carcinoma (dual cell population and true and false lumens) are present but are confined within ducts and lobular units.