April 2016 Case of the Month

58 year-old woman presents with a right breast mass at the 10 o'clock position.  An ultrasound-guided needle core biopsy is performed.  What is your diagnosis?

2X
2X

Low power shows a hypercellular epithelial neoplasm occupying the majority of needle core tissue.

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4X
4X

The neoplasm shows glandular differentiation.

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Vimentin 10X
Vimentin 10X

Vimentin diffusely stains the basaloid cells.

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2X
2X

Low power shows a hypercellular epithelial neoplasm occupying the majority of needle core tissue.

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April 2016 Case of the Month

   Answer: Adenoid Cystic Carcinoma

The morphologic features are consistent with an adenoid cystic carcinoma (ACC).  ACC is usually lumped under the category of "special types" of invasive breast cancer.  This is a relatively rare breast cancer, representing roughly 0.05 - 0.1% of all invasive breast cancers.  The morphology is analogous to ACC tumors that arise in the salivary glands.  The PAS/alcian blue staining features are typical of adenoid cystic carcinoma, and help to distinguish this lesion from invasive cribriform carcinoma, which is the primary differential diagnostic consideration.  Though not shown, this tumor was also negative for ER and PR stains, further lending support to the ACC diagnosis.  ACC has a favorable prognosis with low risk of recurrence after excision and a low risk for distant metastasis.