J Cancer 2020; 11(6):1341-1350. doi:10.7150/jca.40817

Research Paper

Outcomes after Treatment of Metaplastic Versus Other Breast Cancer Subtypes

Amy C. Moreno1, Yan Heather Lin2, Isabelle Bedrosian3, Yu Shen2, Gildy V. Babiera3, Simona F. Shaitelman1✉

1. Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX.
2. Department of Biostatistics, The University of Texas MD Anderson Cancer Center, Houston, TX.
3. Department of Surgical Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX.

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Moreno AC, Lin YH, Bedrosian I, Shen Y, Babiera GV, Shaitelman SF. Outcomes after Treatment of Metaplastic Versus Other Breast Cancer Subtypes. J Cancer 2020; 11(6):1341-1350. doi:10.7150/jca.40817. Available from http://www.jcancer.org/v11p1341.htm

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Purpose: Metaplastic breast cancer (BC) is an uncommon yet aggressive histologic subtype of BC. We sought to identify factors associated with its diagnosis and compare the management and outcomes of metaplastic BC with those of other BCs and triple negative invasive ductal carcinoma in particular given how often it has a triple negative phenotype.

Patients and Methods: We identified women diagnosed with invasive BC in 2010-2014 in the National Cancer Data Base, and used univariate analysis to compare baseline patient and tumor characteristics by BC subtype. Overall survival (OS) was estimated with the Kaplan-Meier method, and multivariate Cox proportional hazards models were used to identify independent predictors of OS.

Results: Of 247,355 cases, 2,084 (0.8%) were metaplastic BC, 55,998 (23%) triple negative BC, and 77% other BC. Relative to non-metaplastic BC, women with metaplastic BC were more likely to be older at diagnosis (median age, 62 vs. 59 years), have ≥1 comorbid conditions (22% vs. 18%), and be on Medicare (41% vs. 33%; P<0.001). Metaplastic BCs tended to be basal-like (77%), and relative to triple-negative or other BC, metaplastic BC was associated with higher clinical T status (cT3-4, 18% vs. 11%, 8%), no clinical nodal involvement (cN0, 86%, 77%, 80%), no lymphovascular invasion (72%, 65%, 62%), and high-grade tumors (71%, 77%, 35%) (P<0.001). Most metaplastic BCs were treated with mastectomy (58%), sentinel lymph node dissection (65%), chest wall or breast irradiation (74%), and chemotherapy (75%) as adjuvant therapy (60%). At a median follow-up time of 44.5 months, OS rates were lower for metaplastic BC than for triple-negative or other BC across all clinical stages at 5 years (stage I, 85%, 87%, 91%; II, 73%, 77%, 87%; III, 43%, 53%, 75%) and at 3 years (Stage IV, 15%, 22%, 64%; P<0.001). On multivariate analysis, increasing age, advanced clinical stage, lymphovascular invasion, axillary (vs. sentinel) node dissection, and no radiation or chemotherapy were associated with worse outcomes in metaplastic BC. Extent of surgery affected survival for triple-negative and other BC but not for metaplastic BC.

Conclusion: Outcomes for metaplastic BC continue to be worse than those for other BC subtypes despite modern treatments. Optimizing systemic therapy options, which was a significant predictor of survival, should be a priority in managing metaplastic BC.

Keywords: metaplastic breast cancer, triple negative breast cancer, breast cancer outcomes, radiation therapy, chemotherapy.