Comprehensive clinicopathologic analysis and management approaches for metaplastic breast cancer: A retrospective, single institution study.

Abstract

e13176 Background: Metaplastic breast cancer (MpBC) is a rare and aggressive subtype of breast cancer characterized by its heterogeneous histology and poor prognosis. Effective systemic therapies for both definitive and salvage treatment remain poorly defined. Due to the rarity of MpBC, the relationship between its clinicopathologic features, optimal therapeutic strategies, and patient outcomes are largely understudied. Methods: This study is a single-center, retrospective analysis of patients with MpBC treated at Cedars-Sinai Medical Center between 2004-2023. Patients were identified using the Cancer Registry database. The primary outcomes are overall survival (OS) and disease-free survival (DFS). All endpoints were evaluated utilizing the Kaplan-Meier method. Hazard ratios (HR) were estimated using a stratified Cox proportional-hazards model. All reported 95% confidence intervals (CI) are two-sided. Results: Of 81 patients with MpBC identified, the median age at diagnosis was 63 years (range 27-98). 65.4% were White, 27.2% were Black, 6.2% were Asian, and 4.9% were Hispanic. 76.5% (n = 62) had triple negative BC (TNBC) (ER < 1% and HER2 negative by ASCO CAP guidelines), 17.2% (n = 14) had hormone receptor positive (HR+), HER2 negative (HER2-) disease, 2.4% (n = 2) had HR-HER2+ disease, 3 were unknown. At diagnosis, 67.6% (n = 48) had Stage I/II disease, 25.3% (n = 18) had Stage III disease, 7.0% (n = 5) had de novo stage IV MpBC, 10 were unknown. 13 patients had squamous morphology, 8 had mesenchymal, 4 had mixed, 2 had spindle cell, and 54 had NOS (not otherwise specified) subtype. Of the 17 patients who underwent genetic testing, 6 patients tested positive for a BRCA mutation. Of the 66 early-stage patients with available treatment records, 30.3% (n = 20) received neoadjuvant systemic therapy, all underwent surgical resection, 75.7% (n = 50) received adjuvant radiation therapy, and 60.6% (n = 40) received adjuvant chemotherapy. In the entire cohort, the 5-year OS was 68% and 5-year DFS was 62%. 5-year OS by stage is as follows: Stage I: 100%, II: 82.0%, and III: 46.6%. 5-year DFS is as follows: Stage I: 100%, II: 79.6%, and III: 42.3%. Multivariate Cox proportional analysis showed an OS benefit in patients who received adjuvant chemotherapy (HR 0.30, CI 0.10-0.85, p = 0.024) and in patients who received adjuvant radiation therapy (HR 0.31, CI 0.10-0.98, p = 0.046). Of the patients who received adjuvant chemotherapy, the most commonly used regimen was AC-T (Adriamycin, Cytoxan, and Taxol) at 47.5% (n = 19). Conclusions: Our dataset demonstrates that adjuvant chemotherapy and radiation therapy confer a significant overall survival benefit in patients with MpBC. Additional prospective data and randomized control studies are warranted to determine the most effective treatment strategies for this rare subtype of breast cancer.