Fibromatosis-Like Metaplastic Triple-Negative Breast Cancer: A Case Report.

Fibromatosis-like metaplastic carcinoma (FLMC) is an extremely rare subtype of metaplastic breast carcinoma that closely resembles desmoid-type fibromatosis histologically, making it one of the most diagnostically challenging breast lesions. In contrast to most triple-negative breast cancers, FLMC follows a relatively indolent clinical course, though local recurrence is well documented, and because so few cases have been reported, no established treatment guidelines exist and the role of chemotherapy remains uncertain. We present the case of a 63-year-old woman recalled from routine screening digital breast tomosynthesis for an irregular, spiculated mass in the right breast, confirmed on biopsy to be FLMC, and treated with breast-conserving surgery and adjuvant radiation therapy without chemotherapy after two medical oncologists gave opposing recommendations regarding systemic treatment. She has remained without evidence of disease at two-year follow-up. This case adds to the limited literature on FLMC, supports surgery and radiation alone as a potentially effective treatment strategy in carefully selected patients, and highlights the importance of recognizing FLMC as a biologically distinct entity that should not be managed the same way as conventional triple-negative breast cancer, though longer-term follow-up is needed given the limited data on treatment outcomes for this rare tumor.