Spindle cell carcinoma of the breast resembling pseudoangiomatous stromal hyperplasia.

Pseudoangiomatous stromal hyperplasia (PASH) is commonly present in gynaecomastia, can be seen in some mammary fibroepithelial lesions and in fibrocystic change, and rarely forms a mass. Spindle cell carcinoma of the breast can have a wide range of appearances. This case series describes five spindle cell carcinomas of the breast resembling PASH, a pattern that does not appear to have been reported before. All had bland nuclei like those in fibromatosis-like spindle cell carcinoma. All cases had more close-packed areas, but this was only a very minor component in the index case. Two had associated ductal carcinoma in situ. All were cytokeratin positive with immunohistochemistry. The similarity of the carcinomas in this series to PASH is a diagnostic pitfall particularly in core biopsies as more cellular areas may be only focal.