Desmoid-Type Fibromatosis of the Male Breast Associated with Bilateral Gynecomastia: Diagnostic Challenges and...

Background/Objectives: Breast fibromatosis (desmoid-type fibromatosis) is a rare, locally aggressive neoplasm that may closely mimic breast carcinoma on imaging. Occurrence in male patients is exceptionally uncommon, particularly in association with gynecomastia. We report a rare case of male breast fibromatosis and discuss the diagnostic challenges, surgical decision-making, and reconstructive management. Methods: A 35-year-old male presented with a palpable right breast mass and bilateral grade II gynecomastia. Histopathological and immunohistochemical analyses were performed. Following multidisciplinary evaluation, the patient underwent wide local excision of the lesion with immediate glandular-adipose tissue rearrangement and simultaneous contralateral gynecomastia correction. Results: Ultrasonography demonstrated a hypoechoic lesion of 12 × 11 mm, whereas mammography revealed an irregular mass measuring up to 34 mm. Core needle biopsy showed a fibroblast-rich spindle-cell proliferation with nuclear β-catenin positivity, consistent with desmoid-type fibromatosis. Final histopathology confirmed a 2.5 cm lesion with negative resection margins (minimum margin 5 mm). Immediate reconstruction achieved a satisfactory chest contour and symmetry. No evidence of recurrence was observed during 18 months of follow-up. Conclusions: Breast fibromatosis should be considered in the differential diagnosis of suspicious male breast lesions because radiological findings may closely resemble breast carcinoma. Histopathological confirmation remains essential for appropriate management. In selected patients, immediate glandular-adipose tissue rearrangement may facilitate single-stage defect reconstruction and preservation of chest contour following oncologic excision.