A Peculiar Pattern

 
Low power shows expansion of ducts and lobular units.

Low power shows expansion of ducts and lobular units.

At higher magnification, a cellular proliferation is evident that involves several lobular units and adjoining ducts. 

At higher magnification, a cellular proliferation is evident that involves several lobular units and adjoining ducts. 

Small lumens with eosinophilic material are formed by the cellular proliferation.

Small lumens with eosinophilic material are formed by the cellular proliferation.

A dual cell population is present with basal-type cells especially prominent at the periphery of the tumor nests.  True and false lumens can also  be seen.

A dual cell population is present with basal-type cells especially prominent at the periphery of the tumor nests.  True and false lumens can also  be seen.

DIAGNOSIS:  Adenoid cystic carcinoma in situ

DISCUSSION:

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.