Personal and clinical social support and adherence to adjuvant endocrine therapy among hormone receptor-positive breast cancer patients in an integrated health care system.

Purpose: We evaluated associations between personal and clinical social support and non-adherence to adjuvant endocrine therapy (AET) in a large, Northern California breast cancer (BC) cohort from an integrated healthcare network.

Methods: This study included 3382 women from the Pathways Study diagnosed from 2005 to 2013 with stages I-III hormone receptor-positive BC and who responded to the Medical Outcomes Study Social Support and Interpersonal Processes of Care surveys, approximately 2 months post-diagnosis. We used logistic regression to evaluate associations between tertiles of social support and non-initiation (< 2 consecutive prescription fills within a year after diagnosis). Among those who initiated treatment, we used proportional hazards regression to evaluate associations with discontinuation (≥ 90 day gap) and non-adherence (< 80% medical possession ratio).

Results: Of those who initiated AET (79%), approximately one-fourth either discontinued AET or were non-adherent. AET non-initiation was more likely in women with moderate (adjusted OR 1.18, 95% CI 0.96-1.46) or low (OR 1.30, 95% CI 1.05-1.62) versus high personal social support (P trend = 0.02). Women with moderate (HR 1.20, 95% CI 0.99-1.45) or low (HR 1.32, 95% CI 1.09-1.60) personal social support were also more likely to discontinue treatment (P trend = 0.01). Furthermore, women with moderate (HR 1.25, 95% CI 1.02-1.53) or low (HR 1.38, 95% CI 1.12-1.70) personal social support had higher non-adherence (P trend = 0.007). Associations with clinical social support and outcomes were similar. Notably, high clinical social support mitigated the risk of discontinuation when patients' personal support was moderate or low (P value = 0.04).

Conclusions: Women with low personal or clinical social support had higher AET non-adherence. Clinician teams may need to fill support gaps that compromise treatment adherence.