Unraveling Fibromatosis-Like Metaplastic Breast Carcinoma: Insights from a Multicenter Cohort and Survival Benchmarking
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Fibromatosis-like metaplastic carcinoma (FLMC) is a rare and distinct subtype of metaplastic breast carcinoma (MBC), comprising 4–8% of cases. Characterized by a triple-negative receptor profile and low proliferative activity, FLMC exhibits less aggressive clinical behavior compared to other MBC subtypes. However, due to its rarity, knowledge of its clinical and pathological features, treatment outcomes, and prognosis remains limited. This multicenter retrospective cohort study included 21 FLMC cases diagnosed between November 2016 and November 2024 at two tertiary cancer centers in China. Data on clinical presentation, pathology, treatment, and outcomes were collected and analyzed. Disease-free survival (DFS) and overall survival (OS) were estimated using the Kaplan-Meier method. A matched cohort of spindle cell carcinoma (SCC) patients was analyzed for comparative survival outcomes.The median age of FLMC patients was 59 years (IQR: 45–77). All tumors were triple-negative (ER-/PR-/HER2-) and exhibited a low Ki-67 proliferation index in 43% of cases. Lymph node metastasis was observed in only one patient (4.8%). Surgery was the primary treatment modality, with breast-conserving surgery and adjuvant radiotherapy showing improved DFS. Neoadjuvant chemotherapy demonstrated limited efficacy, with poor outcomes in one patient. The 3-year DFS and OS rates for FLMC were 95.2% and 90.5%, respectively, significantly higher than those for SCC (DFS: 81.0%; OS: 76.2%; p < 0.05). FLMC is an indolent MBC subtype with a favorable prognosis and low risk of recurrence or metastasis. Surgical resection remains the cornerstone of treatment, with selective use of adjuvant therapies based on tumor characteristics. Neoadjuvant chemotherapy is not recommended due to limited benefit. Future research should focus on prospective validation of these findings, molecular profiling, and exploration of novel systemic therapies for this rare entity.
