• Xuexin He, Jiali Ji, Rongrong Dong, Hong Liu, Xiaolan Dai, Chongjian Wang, Francisco J Esteva, and YeungSai-Ching JimSJDepartment of Endocrine Neoplasia and Hormonal Disorders, The University of Texas MD Anderson Cancer Center, Houston, TX, USA. syeung@mdanderson.org.Department of Emergency Medicine, The University of Texas MD Anderson Cancer Center, 1.
• Department of Medical Oncology, The 2nd Affiliated Hospital, School of Medicine, Zhejiang University, No. 88 Jiefang Rd, Hangzhou, Zhejiang, 310010, China. xuexinhe@zju.edu.cn.
• Breast Cancer Res. Treat. 2019 Jan 1; 173 (2): 329-341.

BackgroundMetaplastic breast cancer (MpBC) is a rare histological subtype of breast cancer recognized as a unique pathologic entity in 2000. However, the pathogenesis, optimal therapy, and prognosis of MpBC and the potential effect of systemic treatments on different subtypes of MpBC are not well defined.MethodsA retrospective population-based study was performed to identify breast cancer patients with MpBC and other triple-negative breast cancers (TNBC) between 2010 and 2014 using the surveillance, Epidemiology, and End Results (SEER) database. Chi-square test was used to analyze characteristics between subgroups. Kaplan-Meier analysis and Multivariate Cox regressions were used to evaluate overall survival (OS) of MpBC, TNBC, and MpBC subgroups. Competing risk analysis and multivariate regression model of competing risk were used to assess breast cancer-specific survival (BCSS) of MpBC and TNBC RESULTS: We identified a study cohort of 22,433 patients (1112 MpBC and 21,321 TNBC). MpBC correlated with older population, larger tumor size and less lymph node involvement, and TNBC phenotype. Patients with MpBC especially with triple-negative subtype (TN-MpBC) had worse survival than the overall TNBC population. However, the prognosis of MpBC without triple-negative subtype (non-TN MpBC) was not different from that of TNBC. In Kaplan-Meier analysis, chemotherapy was not associated with significant difference in OS of TN-MpBC. In non-TN MpBC group, the 3-year OS was 79.8% for patients receiving chemotherapy and 70.5% in patients without chemotherapy, and chemotherapy was associated (P = 0.033) with improved OS. Within the MpBC patients, radiotherapy was significantly (HR 1.544; 95% CI 1.148-2.078; P = 0.004) associated with improved OS and (HR 1.474; 95% CI 1.067-2.040; P = 0.019) BCSS.ConclusionsPatients with TN-MpBC had worse prognosis than TNBC and chemotherapy was not associated with improved survival. In contrast, non-TN MpBC may derive survival benefit from chemotherapy and radiotherapy.

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