Prognostic factors and adjuvant systemic therapy for patients with HER2-positive T1N0 breast cancer: evidence from a real-world study with long-term follow-up

Purpose The optimal adjuvant systemic treatment and potential prognostic factors for patients with T1N0 HER2-positive breast cancer are still unclear. We conducted a real-world study in this relatively low-risk population to identify the clinical-pathological factors of potential prognostic value and to compare the efficacy of different adjuvant strategies. Methods We included patients with HER2-positive T1N0 breast cancer of infiltrating ductal carcinoma (IDC) histology treated at the Cancer Hospital, Chinese Academy of Medical Sciences from April 2010 to April 2017. We performed Cox multivariate analysis to identify the potential prognostic factors for invasive disease-free survival (IDFS). We also compared survival outcomes of (1) patients treated with adjuvant chemotherapy alone, or chemotherapy plus trastuzumab, or observation; (2) patients receiving adjuvant anthracycline-based and non-anthracycline regimens, both combined with trastuzumab. Inverse probability of treatment weighting (IPTW) propensity score was used to reduce selection bias. Results Overall, 692 consecutive patients were included, with a median follow-up of 78.0 months for IDFS. Age ≤ 40, T1c, ER + PR + , and adjuvant trastuzumab were identified as independent prognostic factors. For adjuvant treatment, compared with observation and chemotherapy alone, chemotherapy plus trastuzumab could significantly benefit patients (HR = 2.70, P = 0.034; HR = 3.95, P < 0.001). Meanwhile, compared with observation, chemotherapy alone did not significantly benefit patients (HR = 1.37, P = 0.424). For the comparison of anthracycline-based versus non-anthracycline regimens when combined with trastuzumab, patients in both groups had similar IDFS (HR = 1.74, P = 0.242). Conclusions HER2-positive T1N0 IDC patients could benefit from adjuvant chemotherapy plus trastuzumab. Age ≤ 40, T1c, ER + PR + , and adjuvant trastuzumab are independent prognostic factors for this population.