1534 - Predictors of adherence among post-menopausal women receiving adjuvant endocrine therapy for breast cancer in Ontario, Canada

Background

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.

Methods

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.

Results

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.

Conclusions

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.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

The authors.

Funding

Academic Medical Association of South Western Ontario (AMOSO).

Disclosure

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.