Associate Professor Auburn University Auburn, United States
Background: Adjuvant endocrine therapy (ET) is the cornerstone of systemic treatment of estrogen receptor (ER)-positive breast cancers. Assessing the effect of adjuvant oral ET on survival in women with early-stage breast cancer can improve uptake and optimize treatment strategies.
Objectives: We assessed the all-cause and breast cancer related mortality of Medicare women with early-stage breast cancer compared to nonusers.
Methods: This retrospective new user cohort study used the 2011-2019 Surveillance, Epidemiology and End Results (SEER)-Medicare data. Female beneficiaries newly diagnosed with hormone receptor (HR)-positive, stage I-III breast cancer in 2012-2017 were included. Beneficiaries who initiated any of the four ET (tamoxifen, anastrozole, letrozole, and exemestane) within 3 months after breast cancer diagnosis were defined as initiators (washout period of 12 months before cancer diagnosis), and those who never initiated these treatments were non-initiators. Patients were followed until death, or December 31, 2019 for all-cause mortality (December 31, 2018 for breast cancer related mortality), or Medicare disenrollment, whichever occurred first. Inverse-probability weighting was used to balance baseline covariates (age, race/ethnicity, geographic region, urbanicity, household income, education level, marital status, comorbidity, ER visit), cancer characteristics (tumor grade/stage, number of reginal nodes, nodal stage, cancer stage, receptor status), and breast cancer screening services (mammography, CT scan/ultrasound) between initiators and non-initiators. Weighted Cox proportional hazard models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) of all-cause and breast cancer related mortality between initiators and non-initiators.
Results: Compared with non-initiators (n=8,899), ET initiators (n=24,289) were more likely to be older, White, married, residing in Northeast, having higher income, less comorbidities/ER visits, lower tumor grade and higher cancer stage, and more likely to receive breast cancer screening services than non-initiators (all P<0.05). Unadjusted results showed that ET initiators had less risk in both all-cause (HR=0.55, 95%CI=0.52-0.57) and breast cancer related mortality (HR=0.46, 0.41-0.52) than non-initiators. After weighting, ET initiation was associated with reduced all-cause (HR=0.62, 0.59-0.66) and breast cancer related mortality (HR=0.57, 0.50-0.64).
Conclusions: Female beneficiaries with early-stage breast cancer may achieve survival benefits when they initiate adjuvant ET treatment early on. Uptake of adjuvant ET among this population should be improved.
