Adjuvant endocrine therapy (AET) is an important treatment for post-menopausal hormone receptor positive breast cancer. We used health administrative data to explore factors associated with AET adherence and survival.
We used health administrative databases to investigate adherence of post-menopausal women (aged ≥ 66 years) who started endocrine therapy from 2005-2010. Adherence was measured by medical possession ratio (MPR) and characterized as low (<40% MPR), intermediate (40-79% MPR) or high (≥80% MPR) over a five-year period. We investigated factors influencing AET adherence using a multinomial logistic regression model and the association with all-cause death (5-years after starting AET) using a multivariable cox-proportional hazards model.
We identified 5,692 eligible patients with a median age of 73 years (IQR: 69-78), 67% received lumpectomy, 33% mastectomy, 26% adjuvant radiation, 13% adjuvant chemotherapy and 70% of patient originally started on an aromatase inhibitor versus tamoxifen. AET adherence was low in 13% (n = 749), intermediate in 13% (n = 733) and high in 74% (n = 4,210) of patients. Lower levels of adherence were observed among older patients [low vs. high adherence: odds ratio (OR)=1.03, 95% CI: 1.02-1.05 (per year); intermediate vs. high adherence: OR = 1.02, 95% CI: 1.01-1.04 (per year)]. High adherence was associated with use of adjuvant chemotherapy (low versus high adherence OR = 0.42 95% CI: 0.30-0.59) and short-term follow-up with a medical oncologist within 4 months of starting AET (low vs. high adherence OR = 0.83, 95% CI: 0.69-0.99). Unadjusted analysis showed an increased risk of death among patients with lower AET adherence [low vs. high adherence: hazard ratio (HR)=1.31, 95% CI: 1.12-1.53 and intermediate vs. high adherence: HR = 1.40, 95% CI: 1.21-1.62]. However, a significant association could no longer be detected after multivariable adjustment.
Non-adherence to endocrine therapy appears to be more common among older breast cancer patients. Short-term follow-up visit by a patient’s medical oncologist after starting AET may help to improve adherence. Developing strategies to optimize endocrine therapy adherence are warranted.
Academic Medical Association of South Western Ontario (AMOSO).
T. Vandenberg: Advisory / Consultancy: Novartis; Advisory / Consultancy: Roche. K. Pritchard: Advisory / Consultancy: Pfizer; Advisory / Consultancy: Roche; Advisory / Consultancy: Amgen; Advisory / Consultancy: Novartis; Advisory / Consultancy: Eisai; Advisory / Consultancy: Genomic Health; Advisory / Consultancy: Myriad Genetics. A. Louie: Advisory / Consultancy: AstraZeneca; Honoraria (self): Varian Medical Systems Inc. J. Raphael: Honoraria (self): Hoffmann La Roche. All other authors have declared no conflicts of interest.