Maintenance endocrine therapy prolonged progression-free survival of first-line chemotherapy with trastuzumab in advanced HR-positive, HER2-positive breast cancer patients.

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e13023 Background: Human epidermal growth factor receptor-2 (HER2) positive breast cancer is a growing concern due to the boom in anti-HER2 therapy. Trastuzumab as the most classic anti-HER2 therapy drug, combined with chemotherapy has become the standard first-line treatment for advanced HER2-positive (HER2+) patients. Although some real-world studies of trastuzumab have been reported, less is known about the role of hormone receptors (HR) in first-line combined therapy. For maintenance therapy after chemotherapy combined with anti-HER2 therapy, the guidance given by clinical trials is the maintenance of targeted therapy. However, for those with HER2+/HR-positive (HR+) breast cancer, whether adding endocrine maintenance therapy can benefit progression-free survival (PFS) in addition to anti-HER2 therapy still needs more research. Thus, the purpose of this study was to retrospectively analyze real-world data, determine the factors that influence the trastuzumab-based therapy in advanced HER2-positive breast cancer patients. Methods: We retrospectively collected the treatment information of advanced breast cancer patients underwent first-line chemotherapy with trastuzumab from 2012 to 2021 in Zhejiang Cancer Hospital. Kaplan–Meier analysis and Cox regression methods were used to calculate and compare the PFS. Results: The study finally enrolled 285 patients meeting the requirement, including 150 HER2+/HR-negative (HR-) and 135 HER2+/HR+ (triple-positive) patients. The median chemotherapy treatment cycles and trastuzumab cycles were 7 (6-8) and 12 (7-17) cycles, respectively. For triple-positive breast cancer, maintenance endocrine therapy was aslo given concurrently with trastusumab in 75 patients after chemotherapy and trastusumab. Overally, the median PFS of first-line treatment was 11.73 (10.16-13.30) months, which was consistent with literature reports. Multivariate analysis revealed that HR positive [hazard ratio, 0.69; 95% confidence interval (CI), 0.52–0.92; P= 0.010], and non-brain metastasis (hazard ratio, 0.54; 95% CI, 0.29–0.99; P= 0.048) were independent prognostic factors. Further Kaplan–Meier analysis demonstrated triple-positive patients with maintenance endocrine therapy significantly had longer PFS than triple-positive patients without maintenance endocrine therapy and HER2+/HR- patients (21.33m vs. 10.13m vs. 9.53m, respectively, P < 0.001). Conclusions: HR-positive was an independent prognostic factor for HER2-positive advanced breast cancer patients receiving first-line chemotherapy with trastuzumab. And endocrine therapy combined trastuzumab as Maintenance after chemotherapy prolonged PFS in HR-positive subgroup patients.