Adjuvant Weekly Paclitaxel and Trastuzumab for HER2-Positive Early-Stage Breast Cancer with Preserved Baseline LVEF: Incidence of Cardiotoxicity and Feasibility of Simplified Cardiac Surveillance

Purpose: The incidence of trastuzumab-related cardiotoxicity is low among patients receiving regimens that do not include anthracyclines. We aimed to examine whether cardiac monitoring during paclitaxel and trastuzumab therapy can be simplified in a strictly defined low-risk population. Patients and Methods: We both retrospectively and prospectively assessed the cardiotoxicity incidence among patients with human epidermal growth factor receptor 2 (HER2)-positive breast cancer treated with adjuvant paclitaxel and trastuzumab, excluding those with major cardiotoxicity risk factors such as a low baseline left ventricular ejection fraction (LVEF). First, records of patients with HER2-positive early-stage breast cancer treated during 2015– 2021 were retrospectively reviewed. Eligibility criteria were as follows: (1) weekly paclitaxel and trastuzumab followed by trastuzumab; and (2) a baseline LVEF ≥ 55%. Second, patients considered suitable for simplified monitoring were prospectively enrolled. Inclusion criteria were a baseline LVEF ≥ 60%, age ≤ 65 years, and body mass index < 30 kg/m 2 . Cardiac function was evaluated every 3 months by using global longitudinal strain (GLS), cardiac biomarkers, and the LVEF. Results: Sixty-six patients were included in the retrospective study. No patients developed symptomatic cardiotoxicity (95% confidence interval CI, 0%– 5.5%). Three patients (4.5%; 95% CI, 1.5%– 12.5%) had an asymptomatic LVEF decline, and all 66 completed the treatment. In the prospective pilot cohort, 9 patients completed therapy, and none developed cardiotoxicity (95% CI, 0%– 29.9%). The median change in the LVEF at 12 months was – 5% (range, – 12% to − 3%), and that in GLS was +2.15% (– 5.5% to +8.3%). No changes in the LVEF or GLS that required treatment interruption occurred, and cardiac biomarkers remained normal. Conclusion: Among patients with HER2-positive early-stage breast cancer who received paclitaxel and trastuzumab, had a preserved baseline LVEF, and had no anthracycline exposure, the cardiotoxicity incidence was low, suggesting that cardiac monitoring may be simplified in this population. Keywords: risk factor, low-risk, cardiac monitoring, anthracycline, global longitudinal strain