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# Seven in ten US women stay on endocrine therapy in the first year, linked claims show
- URL: https://www.coios.me/seven-in-ten-us-women-stay-on-endocrine-therapy-in-the/
- Published: 2026-09-28T06:19:29.000Z
- Updated: 2026-09-28T07:07:29.000Z
- Description: In 401,450 US women initiating adjuvant endocrine therapy for breast cancer, 69.9% had a medication possession ratio of at least 80% in the first year, with modelled behavioural attributes such as comfort following medication instructions weakly associated with adherence after adjustment.
- Author: Daniel Ryan
- Tags: Behavioural science, Adherence and persistence, Cancer, What linked data reveals, United States, #preprint, #refines, #item, #source-2026-09

A retrospective cohort linked longitudinal medical and pharmacy claims to modelled individual-level behavioural and consumer attributes, via privacy-preserving tokenisation, for 401,450 US women who began tamoxifen or an aromatase inhibitor after breast surgery between 2016 and 2025\. Adherence, defined as a medication possession ratio of 80% or more over the first 365 days, was achieved by 280,595 women (69.9%). Behavioural predictors remained significant after adjustment for clinical and demographic factors but were modest in size, including comfort following medication instructions (aOR 1.15, 95% CI 1.06-1.24) and proximity to a breast oncologist (aOR 1.17, 95% CI 1.04-1.32).

*Why it is interesting: It sets a national first-year adherence figure for a therapy whose mortality benefit depends on five to ten years of daily use, and shows what a commercial behavioural-to-claims linkage can and cannot resolve.*

Source

[medRxiv, 26 September 2026](https://doi.org/10.64898/2026.05.25.26353903?ref=coios.me)

DOI

10.64898/2026.05.25.26353903

Type

Preprint

Design

Retrospective cohort, 401,450 US women with invasive breast cancer initiating oral endocrine therapy 2016-2025, claims linked to modelled behavioural scores

Verdict

Refines prior evidence

Driver

[Adherence and persistence](https://www.coios.me/d-adherence/)

Driver

[Cancer](https://www.coios.me/d-cancer/)

Driver

[What linked data reveals](https://www.coios.me/d-linked-data/)