Cost-Effectiveness of Trastuzumab With or Without Chemotherapy as Adjuvant Therapy in HER2-Positive Elderly Breast Cancer Patients: A Randomized, Open-Label Clinical Trial, the RESPECT Trial

Background and Objective: Trastuzumab is a standard care as adjuvant chemotherapy (AdjCT) for patients with human epidermal growth factor receptor 2 (HER2)-positive primary breast cancer (BC) in Japan. However, no reports have evaluated its economics for patients with HER2-positive BC over 70 years of age. The objective of this study was to evaluate the cost-effectiveness of HER2-targeted trastuzumab + chemotherapy in Japan, comparing it with trastuzumab monotherapy. Methods: A three-state-partitioned survival model was developed to evaluate the cost-effectiveness of trastuzumab + chemotherapy versus trastuzumab monotherapy for AdjCT in elderly patients with HER2-positive BC. We derived the efficacy data, utilities, and costs of both arms from individual patient data in the RESPECT trial (NCT01104935) and published studies. The costs and quality-adjusted life years (QALYs) were discounted at 2% per annum using a payer perspective. The respective cost estimates were reported in 2019 Japanese Yen (JPY) or US dollars (US$). The primary outcome was the incremental cost-effectiveness ratio (ICER). We assured robustness with deterministic and probabilistic sensitivity analyses. Results: The cost per patient for trastuzumab + chemotherapy was JPY 14.6 million (US$137,000), and their QALYs were 9.308, compared with JPY 14.2 million (US$131,000) and 9.101, respectively, for trastuzumab monotherapy. The ICER of trastuzumab + chemotherapy versus trastuzumab monotherapy was JPY 2.7 milllion/QALY (US$17,200/QALY). The ICER for trastuzumab with chemotherapy varied from "Dominant" to "Dominated" in one-way sensitivity analysis. Conclusions: The base-case analysis suggests that AdjCT with trastuzumab + chemotherapy is likely to be a cost-effective choice for patients with HER2-positive BC aged 70 years or older. However, the sensitivity analysis suggested uncertainty regarding the cost-effectiveness of trastuzumab + chemotherapy.