Completion versus early discontinuation of chemotherapy and the impact on five-year all-cause mortality in women treated for early-stage breast cancer from 2015-2020: a cohort study using a target trial emulation approach

AIM: Chemotherapy is given for early-stage breast cancer; however, some patients discontinue before completing all planned cycles. This study investigated the impact of early chemotherapy discontinuation on treatment outcomes. METHODS: This retrospective cohort study used a target trial emulation framework to conduct a causal analysis of the all-cause mortality impact of completing a standard course of chemotherapy. Early-stage breast cancer patients treated with chemotherapy in England between 01/01/2014-31/12/2015 were identified from National Disease Registration Service and Systemic Anti-Cancer Therapy datasets. Five-year OS was estimated for patients completing >=six chemotherapy cycles relative to discontinuing chemotherapy early ( =six chemotherapy cycles and 32% (n=3,239) =six cycles showed superior five-year OS compared to discontinuation =six cycles showed improved OS compared to those who discontinued before receiving six cycles. These findings support identification and pre-emptive management of patients at high risk of discontinuing chemotherapy prematurely, to maximise treatment benefit.