Metaplastic Breast Cancer: Practice Patterns, Outcomes, and the Role of Radiotherapy.

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 < 0.001), but not T classification or estrogen receptor status (p > 0.05 for both). Post-lumpectomy RT was associated with higher OS in both the pT1-2N0 and pT3-4/N+ subsets (p < 0.001 for both), while PMRT was associated with OS benefits in pT3-4/N+ cases (p < 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.