RESUMO
PURPOSE: Treating early-stage breast cancer (eBC) may delay or prevent subsequent metastatic breast cancer (mBC). In the phase 3 KATHERINE study, women with human epidermal growth factor receptor 2 (HER2)-positive eBC with residual disease following neoadjuvant therapy containing trastuzumab and a taxane experienced 50% reductions in disease recurrence or death when treated with adjuvant trastuzumab emtansine (T-DM1) vs adjuvant trastuzumab. We predicted the population-level impact of adjuvant T-DM1 on mBC occurrence in five European countries (EU5) and Canada from 2021-2030. METHODS: An epidemiological prediction model using data from national cancer registries, observational studies, and clinical trials was developed. Assuming 80% population-level uptake of adjuvant treatment, KATHERINE data were extrapolated prospectively to model projections. Robustness was evaluated in alternative scenarios. RESULTS: We projected an eligible population of 116,335 women in Canada and the EU5 who may be diagnosed with HER2-positive eBC and have residual disease following neoadjuvant therapy from 2021-2030. In EU5, the cumulative number of women projected to experience relapsed mBC over the 10-year study period was 36,009 vs 27,143 under adjuvant trastuzumab vs T-DM1, a difference of 8,866 women, equivalent to 25% fewer cases with the use of adjuvant T-DM1 in EU5 countries from 2021-2030. Findings were similar for Canada. CONCLUSION: Our models predicted greater reductions in the occurrence of relapsed mBC with adjuvant T-DM1 vs trastuzumab in the indicated populations in EU5 and Canada. Introduction of T-DM1 has the potential to reduce population-level disease burden of HER2-positive mBC in the geographies studied.