Background: Social support is related to treatment and clinical outcomes in breast cancer. We evaluated associations of EHRsupport, an electronic health record (EHR)-based measure of social support, with treatment and clinical outcomes in the full Kaiser Permanente Northern California (KPNC) population of women with breast cancer.

Methods: This study included 45,717 women from KPNC, an integrated health care system, who were diagnosed with invasive breast cancer from January 2006-June 2024 and had social support terms identified in the EHR. The EHRsupport score included information about spouse/partner status, parenthood status, (clinical) visit support, living situation (alone or with others), friend or other support, positive social support, negative (lack of) social support, deceased person, transportation issues, relationship conflict or stress, social isolation, and emergency contact within state. We used log-binomial regression, logistic regression, and survival analysis to evaluate associations of EHRsupport with treatment and survival outcomes.

Results: Lower EHRsupport scores were associated with poorer treatment and clinical outcomes. The lowest (vs. highest) tertile of the EHRsupport score was associated with surgery delays (prevalence ratio (PR)=1.15, 95% confidence interval (CI): 1.11-1.20, p-trend across tertiles <0.001), chemotherapy delays (PR=1.20, 95% CI: 1.10-1.31, p-trend=<0.001), adjuvant endocrine therapy (AET) noninitiation (PR=1.14, 95% CI: 1.10-1.18, p-trend=<0.001), AET discontinuation (HR=1.31, 95% CI: 1.24-1.39, p-trend=<0.001), breast cancer mortality (HR=1.18, 95% CI: 1.08-1.28, p-trend<0.001), and overall mortality (HR=1.21, 95% CI: 1.14-1.29, p-trend<0.001). Comparable associations were seen in women from diverse race and ethnic groups and by cancer stage.

Conclusions: EHRsupport, an EHR-based social support measure, was related to breast cancer treatment and clinical outcomes, supporting its use as a clinical tool and research measure.