• Shun Kawaguchi, Keiichi Kinowaki, Nobuko Tamura, Aya Nishikawa, Akio Shibata, Kiyo Tanaka, Yoko Kobayashi, Takuya Ogura, Junichiro Sato, and Hidetaka Kawabata.
• Department of Breast and Endocrine Surgery, Toranomon Hospital, Tokyo, Japan.
• Medicine (Baltimore). 2022 Dec 16; 101 (50): e32199e32199.

BackgroundSolitary fibrous tumors (SFT) are uncommon mesenchymal neoplasms which can arise in any anatomical location. Pleural SFTs have been most frequently documented; however, breast SFT is an exceedingly rare entity and seldom present in male breast, with only 8 previously reported cases. Recently, STAT6 immunostaining was considered to be a definitive marker of SFT, however, no case of the male breast SFT showing STAT6 positivity preoperatively has been reported.Methods And ResultsWe describe a case of breast SFT in a 73-year-old male patient with a 12-month history of a palpable breast mass. The only associated clinical symptom was bilateral gynecomastia. An ultrasound scan examination revealed an oval, well-circumscribed and hypoechoic mass with hypervascularity. A core-needle biopsy was performed, and microscopic examination with immunohistochemistry confirmed the diagnosis of SFT. He underwent a complete surgical resection with clear margins, and there were no signs of high cellularity, remarkable mitotic activity, pleomorphism, hemorrhage or necrosis.ConclusionA perioperative immunohistochemical evaluation for diffuse and intense nuclear expression of STAT6 was helpful to distinguish SFT from myofibroblastoma. We, herein, describe the first case of SFT in a male breast, confirmed by STAT6 immunostaining positivity. We also conducted a literature review of all previous cases of breast SFTs.Copyright © 2022 the Author(s). Published by Wolters Kluwer Health, Inc.

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