Evaluate whether breast cancer endocrine therapy adherence is affected by access to primary and mental health care, particularly among at-risk patients with mental illness.
The study included 21,892 SEER-Medicare women aged 68 or older with stage I-IV ER+ breast cancer, 2007 to 2013. Patient home counties during breast cancer diagnosis, if evaluated for HPSA care shortage status, were categorized as least, moderate, or highest shortage; unevaluated counties (no known shortage) were a fourth category. Endocrine therapy initiation and discontinuation were analyzed with Cox regression, and daily adherence with longitudinal linear regression.
After multivariate adjustment, patients in high primary care shortage counties were less likely to initiate endocrine therapy, reference least shortage [HR 0.92 (95% CI 0.86-0.97)]. Unevaluated counties had more oncologists per capita, fewer residents below the federal poverty level, and higher incomes. Mental health shortages were not associated with outcomes, however subgroups living in unevaluated counties were less likely to discontinue: patients with bipolar and psychotic disorders [discontinuation HR 0.35 (95% CI 0.17-0.73)], substance use [HR 0.48 (95% CI 0.24-0.95)], anxiety disorders [HR 0.56 (95% CI 0.35-0.90)].
Poor primary care access was associated with a lower likelihood of initiating endocrine therapy but living in counties without established mental health shortages may reduce the harmful association between mental illness and incomplete treatment receipt. Patients with mental illness may be more equipped to complete cancer treatment if given better mental health care access, suggesting a need for care coordination between primary and mental health care.

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