Clinical Characteristics and Survival Outcomes of Metaplastic Breast Carcinoma Subtypes: A Retrospective Study

Introduction: Metaplastic breast carcinoma (MpBC) is a rare neoplasm accounting for < 1% of all breast cancer (BC). It is characterized by histologic and molecular heterogeneity with differentiation into subtypes including squamous cells and/or mesenchymal-like elements, such as spindle, chondroid, and osseous. It is therapeutically challenging and has a worse prognosis than other BC types. Little is known about its different subtypes. Our research evaluated the clinical characteristics and survival outcomes of the various subtypes of metaplastic BC. Methods: This was a retrospective study over 13 y (2010-2023) using the TriNetX database. A total of 558 patients diagnosed with MpBC were identified in the database. The cohort was further queried by subcategories of MpBC (adenosquamous carcinoma, epithelial-myoepithelial carcinoma, adenocarcinoma with squamous metaplasia, adenocarcinoma with cartilaginous and osseous metaplasia, adenocarcinoma with spindle cell metaplasia, metaplastic carcinoma, not otherwise specified [NOS], carcinosarcoma [NOS], myoepithelial carcinoma, and carcinosarcoma, embryonal). Data on demographics, Tumor, Node, and Metastasis stage, treatments (radiation, mastectomy, hormone therapy, immunotherapy, lymph node biopsy/aspiration, chemotherapy), and biomarkers (estrogen receptors, progesterone receptors, human epidermal growth factor receptor 2/neu) were analyzed. A Kaplan–Meier analysis was used to compare overall survival between all the subtypes. A Fisher exact test was used to compare subtypes. Results: Among 558 MpBC patients, the majority were metaplastic carcinoma, NOS (n = 446), followed by carcinosarcoma (n = 49), adenosquamous carcinoma (n = 26), and osseous-differentiated adenocarcinoma (n = 11). Most tumors were triple-negative and Stage I-II. Chemotherapy and mastectomy were common, though treatment patterns varied by subtype. Survival was significantly worse for carcinosarcoma compared to both metaplastic carcinoma, NOS (P = 0.005) and osseous subtypes (P = 0.0039). Median survival was 6.4 y for metaplastic carcinoma NOS and 5.5 y for carcinosarcoma. No deaths occurred in the osseous group. Conclusions: MpBC has a variety of subtypes, and despite its poor prognosis, little research has been conducted, which warrants further investigation.