Micropapillary Mimic

A 59 year old woman underwent excision for a breast density.  Concern about the micropapillary epithelial proliferation was the reason for consultation.

Image 1.  Dense stromal fibrosis surrounds a lobular unit that contains an epithelial proliferation.

Image 2.  the dense stroma has flattened pseudovascular spaces.  micropapillary projections are present within the lobular unit.  

Image 2.  Although the epithelial proliferation is exuberant, the micropapillae are thin and tapering, reminiscent of the hyperplasia seen in gynecomastia.  nuclei are variable, and cellular overlap is evident.  the tips of the micropapillae contain pyknotic cells

Diagnosis:  Usual hyperplasia without atypia, with epithelial and stromal changes similar to patterns seen in gynecomastia.

Discussion:  The stromal fibrosis was responsible for the breast density.  Although some of the stromal changes resemble pseudoangiomatous stromal hyperplasia (PASH), the changes are limited, and associated with a pattern of hyperplasia similar to that seen in men having gynecomastia.  Thin, tapering micropapillae with occasional pyknotic nuclei are characteristic of this pattern of usual (non-atypial) hyperplasia.