Spontaneous Regression (SR) of Male Breast Cancer (MBC): A Rare Case Highlighting Diagnostic Pitfalls and Management Caution.

Background: Male breast cancer (MBC) is rare, accounting for only 1.8% of all breast cancer cases diagnosed globally. However, there is a rising trend in its incidence over the past decades. Spontaneous regression (SR) of a tumor, on the other hand, is a rare but well-documented phenomenon. Case Presentation: We reported a case of MBC that showed SR in the surgical specimen after the histopathologic diagnosis of invasive breast cancer in the core needle biopsy sample. A 58-year-old gentleman presented with a palpable left retroareolar mass, nipple retraction and intermittent pain for 2 months. Imaging and histopathological examination (HPE) confirmed an estrogen- and progesterone-receptor-positive, HER-2 negative invasive carcinoma, which was treated with left mastectomy with axillary clearance (MAC). Intraoperatively, no breast mass was palpable, and SR of the tumor was reported for the surgical sample. Conclusion: This case not only emphasizes the rarity of MBC but also draws attention to the exceptional phenomenon of SR in invasive carcinoma. Recognition of such rare events underscores the importance of cautious decision-making, multidisciplinary management, and further research into the biological and immunological mechanisms underlying tumor regression.