Purpose: Metaplastic breast cancer (MBC) is a rare, aggressive form of breast cancer with limited data to guide management. This study of a large, contemporary US database described national practice patterns and addressed the impact of radiotherapy (RT) on survival. Methods: The National Cancer Data Base was queried (2004–2013) for women with non-metastatic MBC. Multivariable logistic regression ascertained factors associated with RT administration. Kaplan–Meier analysis evaluated overall survival (OS) between patients treated with either lumpectomy or mastectomy with or without RT, while substratifying patients into pT1–2N0 and pT3–4/N+ subcohorts. Cox proportional hazards modeling determined variables associated with OS. Results: Of 5211 total patients, 447 (9%) had lumpectomy alone, 1831 (35%) had post-lumpectomy RT, 2020 (39%) had mastectomy alone, and 913 (18%) had post-mastectomy RT (PMRT). Most patients underwent chemotherapy (79%), and mastectomy was the most common surgical approach (56%). RT delivery was impacted by many factors, including higher nodal disease (p OpenSPiltSPi 0.001), but not T classification or estrogen receptor status (p CloseSPigtSPi 0.05 for both). Post-lumpectomy RT was associated with higher OS in both the pT1–2N0 and pT3–4/N+ subsets (p OpenSPiltSPi 0.001 for both), while PMRT was associated with OS benefits in pT3–4/N+ cases (p OpenSPiltSPi 0.001), but not in pT1–2N0 cases (p = 0.259). Conclusions: In the largest study to date evaluating MBC, practice patterns of surgery, systemic therapy, and RT are described. The addition of RT in the post-lumpectomy setting was associated with higher OS, in addition to pT3–4/N+ in the post-mastectomy setting. Although not implying causation, further work is required to corroborate the conclusions herein.
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