A 32-year-old woman presented with a palpable retroareolar right breast mass. Ultrasound examination showed a well-circumscribed mass measuring 2 cm in the greatest dimension at the 5:00 position. She underwent a biopsy and a subsequent local excision.
The correct answer is ...
Adenoid cystic carcinoma.
Adenoid cystic carcinoma (AdCC) of the breast is a rare entity, and it usually presents in elderly women as a palpable mass, but it can affect younger women and men as well. The retroareolar region is the most frequently affected site but it can arise in any quadrant. Complete excision with negative margins is recommended. Lymph node metastasis and recurrence are rare.
Histologically, AdCC is an invasive carcinoma composed of neoplastic epithelial and myoepithelial cells. It is arranged in tubular, cribriform and solid patterns and it is associated with basophilic matrix. Three subtypes have been defined: classic AdCC, solid-basaloid AdCC, and AdCC with high-grade transformation. Immunoperoxidase studies demonstrate two distinct cell populations. Myoepithelial cells, which are positive for p63, smooth muscle actin, calponin and cytokeratins 14 and 17. Not all tumors will be positive for all myoepithelial markers. Luminal cells are positive for low molecular weight keratins, epithelial membrane antigen, carcinoembryonic antigen, and CD117. AdCC is predominantly negative for ER, PR and Her2. The most common finding is a chromosomal translocation: t(6;9)(q22-23;p23-24) resulting in a MYB-NFIB gene fusion.
An important differential diagnosis is collagenous spherulosis (CS). Both AdCC and CS are composed of myoepithelial and luminal cells. Myoepithelial cells in CS are often positive for multiple immunohistochemical markers. Luminal cells are less likely to be positive for CD117 and are more frequently positive for ER and PR in CS. Other differential diagnoses include cylindroma, adenomyoepithelioma, ductal carcinoma in situ with a cribriform pattern, invasive cribriform carcinoma, and basal-like breast carcinoma.
Patricija Zot, M.D.
Fellow, Surgical Pathology
Charles Sturgis, M.D.
Senior Associate Consultant, Anatomic Pathology
Professor of Laboratory Medicine and Pathology
Mayo College of Medicine and Science