Adjuvant trastuzumab without chemotherapy for treating early HER2-positive breast cancer in older patients: A propensity score-adjusted analysis of a prospective cohort study

<title>Abstract</title> <p><bold>Purpose </bold>To gauge the effects of treatment practices on prognosis for all older patients with HER2-positive early breast cancer, particularly to determine whether adjuvant trastuzumab alone can offer benefit over no adjuvant therapy. This report accompanies the RESPECT study, a randomized-controlled trial (RCT) comparing trastuzumab monotherapy with trastuzumab-plus-chemotherapy.<bold>Patients and methods </bold>Patients who declined the RCT were treated based on the physician’s discretion. We studied the (1) trastuzumab-plus-chemotherapy group, (2) trastuzumab-monotherapy group, and (3) non-trastuzumab group (no therapy or anticancer therapy without trastuzumab). The primary endpoint was disease-free survival (DFS), which was compared using the propensity-score method. Relapse-free survival (RFS) and health-related quality of life (HRQoL) were also assessed.<bold>Results </bold>We enrolled 123 eligible patients, aged over 70 years, with HER2-positive invasive breast cancer in this cohort study. The median age was 74.5 years. Among cohort study treatment categories were as follows: (1) trastuzumab-plus-chemotherapy group (n = 36, 30%), (2) trastuzumab-monotherapy group (n = 52, 43%), and (3) non-trastuzumab group (n = 32, 27%). A total of 73% of patients received trastuzumab-containing regimens, with or without chemotherapy. The 3-year DFS was 92.3% in the trastuzumab-plus-chemotherapy group, 89.2% in the trastuzumab-monotherapy group, and 82.5% in the non-trastuzumab group. DFS in the non-trastuzumab group was lower than in the trastuzumab-plus-chemotherapy and trastuzumab-monotherapy groups (propensity-adjusted HR: 3.29; 95% CI: 1.15–9.39; <italic>P</italic> = 0.026). The RFS in the non-trastuzumab group was lower than in the trastuzumab-plus-chemotherapy and trastuzumab monotherapy groups (propensity-adjusted HR = 7.80; 95% CI: 2.32–26.2, <italic>P</italic> < 0.0001). There were no significant intergroup differences in the proportions of patients showing QoL deterioration (<italic>P </italic>= 0.717) and improvement (<italic>P </italic>= 0.652) at 36 months.<bold>Conclusions</bold> Trastuzumab-treated patients had better prognoses than patients not treated with trastuzumab without deterioration of HRQoL. Thus, trastuzumab monotherapy can be considered for patients who reject chemotherapy.<bold>Trial registration number </bold>The protocol was registered on the website of the University Hospital Medical Information Network (UMIN), Japan (protocol ID: UMIN 000028476).</p>