Outcomes of Patients with ER+/HER2+ Nonmetastatic Breast Cancer Treated with Trastuzumab without Chemotherapy

The efficacy of trastuzumab monotherapy in HER2+ breast cancer is limited, and, thus, standard of care is to combine trastuzumab with chemotherapy (CT). For patients who cannot tolerate CT, there is no randomized data comparing trastuzumab + hormone therapy versus hormone therapy alone in the nonmetastatic setting. At SABCS 2019, the authors examined the outcomes of nonmetastatic HER2+ breast cancer patients treated with trastuzumab without chemotherapy in the National Cancer Database.1 

In 46,025 patients with clinical stage I-III ER+/HER2+ breast cancer who received surgery, the authors compared the efficacy of CT, adjuvant hormone therapy alone (HT), combination HT + trastuzumab (HT + T), and no adjuvant treatment (NT). The median follow-up was 31 months for CT, 30 months for HT, 30 months for HT + T, and 27 months for NT. Most patients received standard of care with CT (78%; n = 36,008), 12% (n = 5632) received adjuvant HT (HT), 3% (n = 1157) were treated with HT + T, and 12% (n = 2669) received NT. There was a higher representation of elderly patients aged >70 years in the HT (41%), HT + T (51%), and NT (38%) arms compared with the CT arm (13%). There was a higher representation of lobular histology in the HT + T arm (52%) compared with the CT (11%), HT (11%), or NT (11%) arms. There was a higher representation of node-positive patients (N1-3 vs N0) in the CT (38%) and HT + T (27%) groups versus the HT (13%) and NT (16%) arms. Similarly, there were more patients with high-grade disease (grade 3) and lymphovascular invasion (+LVI) in the CT (48% grade 3, 25% +LVI) and HT + T (45% grade 3, 20% +LVI) arms versus in the HT (30% grade 3, 12% +LVI) and NT (39% grade 3, 15% +LVI) arms. Medicare patients were more likely to be treated with HT + T (58%) or HT (50%) than CT (24%) or no HT (45%), probably due to older age.

Compared with the standard-of-care CT arm, the patients treated without CT had significantly worse overall survival (OS). There was no improvement in OS for HT + T versus HT without T. Hazard ratios for treatment regimens without CT were significantly worse with a hazard ratio of 2.26 for HT without T, 3.01 for HT + T, and 4.37 for NT (P <.0001). 

In this largest retrospective analysis of US patients with ER+/HER2+ nonmetastatic breast cancer, the study failed to identify an OS benefit with HT + T compared with HT alone, although further analysis including a multivariate analysis and propensity score matching will be performed in the future.

Reference

1. Nguy S, et al. SABCS 2019. Abstract P1-18-02.

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