ZC3H7B-BCOR Primary Breast Sarcoma: Diagnostic and Therapeutic Challenges of an Ultra-rare Sarcoma in an Uncommon Location

Primary breast sarcomas (PBS) are rare mesenchymal malignancies, accounting for <1% of all breast neoplasms. The diagnostic process for PBS is challenging in young women, mainly due to their similarity with prevalent benign breast conditions regarding clinical and imaging features. Their treatment is also complex, given their typically aggressive clinical behavior, extreme rarity, and the lack of established guidelines for their management. BCOR-rearranged sarcomas, including those harboring the ZC3H7B–BCOR fusion, represent an ultra-rare subtype with distinct clinical, histopathological, and molecular features, most commonly described in the endometrial stroma. We report the case of a 20-year-old woman with a PBS harboring a ZC3H7B-BCOR fusion (to our knowledge, the first reported case of a PBS with this molecular alteration). The complexity of its diagnostic process and the numerous unique challenges faced throughout its therapeutic management are emblematic and highlight the importance of multidisciplinary and international collaboration.