Abstract Introduction Despite universal access to oncology care, social disparities in cancer survivorship persist in Denmark. For premenopausal women with estrogen receptor-positive breast cancer, decisions regarding extending endocrine therapy beyond five years often depend on estimated individual recurrence risk and treatment tolerance. We examined whether social disparities are associated with the initiation of extended endocrine therapy among Danish breast cancer survivors who were recurrence-free at five years post-diagnosis. Methods We included all women registered in the Danish Breast Cancer Group clinical database who were premenopausal at diagnosis with a first primary, estrogen receptor-positive, stage I-III invasive breast cancer diagnosed during 2008-2011. We further restricted the population to those who initiated adjuvant endocrine therapy and were alive, recurrence-free, and residing in Denmark five years after diagnosis. Extended endocrine therapy was defined as cumulative coverage with endocrine therapy for at least one year beyond the initial five years of treatment. Using the unique personal registration number assigned to all Danish residents, we linked patients across nationwide registries to obtain information on cohabitation, marital status, employment, income, and education, measured at or before endocrine therapy initiation. Associations between social characteristics and treatment extension were estimated using logistic regression, adjusted for patient age at diagnosis, and reported as odds ratios (ORs) with 95% confidence intervals (CIs). Results Among 1,911 premenopausal patients diagnosed during the study period, 1,136 (57%) continued endocrine therapy beyond five years. Treatment extension varied across all assessed social characteristics. Women living alone at endocrine therapy initiation were less likely to extend (OR = 0.64; 95% CI, 0.51-0.79) compared with those cohabiting with a partner. Similarly, unmarried women (OR = 0.70; 95% CI, 0.55-0.90) and those who were divorced or widowed (OR = 0.67; 95% CI, 0.52-0.87) had lower rates of extension compared with married women. Survivors who were unemployed (vs employed; OR = 0.66; 95% CI, 0.52-0.83) or in the lowest quartile of household income (vs highest; OR = 0.72; 95% CI, 0.55-0.94) also had reduced odds of treatment extension. Finally, women with short education had 0.79 (95% CI, 0.61-1.02) times the odds of extension compared with those with long education. Conclusions Our study suggested differences in the uptake of extended endocrine therapy according to social characteristics. Future work will build on these findings to evaluate how social and clinical factors together influence long-term treatment adherence and recurrence outcomes, with the aim of informing more equitable survivorship care. Citation Format: Kirsten M. Woolpert, Lene Mellemkjær, Søren Friis, Mette Nørgaard, Bent Ejlertsen, Deirdre Cronin-Fenton. Social disparities in the extension of endocrine therapy among premenopausal breast cancer survivors in Denmark abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 3676.
Woolpert et al. (Fri,) studied this question.