Association of diabetes and diabetes treatment with incidence of breast cancer

AIMS: The aim of this study was to evaluate the association of diabetes and diabetes treatment with risk of postmenopausal breast cancer. METHODS: Histologically confirmed incident cases of postmenopausal breast (N = 916) cancer were recruited from 23 Spanish public hospitals. Population-based controls (N = 1094) were randomly selected from primary care center lists within the catchment areas of the participant hospitals. ORs (95 % CI) were estimated using mixed-effects logistic regression models, using the recruitment center as a random effect term. Breast tumors were classified into hormone receptor positive (ER+ or PR+), HER2+ and triple negative (TN). RESULTS: Diabetes was not associated with the overall risk of breast cancer (OR 1.09; 95 % CI 0.82-1.45), and it was only linked to the risk of developing TN tumors: Among 91 women with TN tumors, 18.7 % were diabetic, while the corresponding figure among controls was 9.9 % (OR 2.25; 95 % CI 1.22-4.15). Regarding treatment, results showed that insulin use was more prevalent among diabetic cases (2.5 %) as compared to diabetic controls (0.7 %); OR 2.98; 95 % CI 1.26-7.01. They also showed that, among diabetics, the risk of developing HR+/HER2- tumors decreased with longer metformin use (ORper year 0.89; 95 % CI 0.81-0.99; based on 24 cases and 43 controls). CONCLUSION: This study reinforces the need to correctly classify breast cancers when studying their association with diabetes. Given the low survival rates in women diagnosed with TN breast tumors and the potential impact of diabetes control on breast cancer prevention, more studies are needed to better characterize this association.This work was supported by research Grants from Spain´s Health Research Fund Fondo de Investigación Sanitaria (PI12/00488, PI08/1770, PI08/0533, PI08/1359, PS09/00773, PS09/01286, PS09/01903, PS09/02078, PS09/01662, PI11/01403, PI11/01889, PI11/00226, PI11/01810, PI11/02213, PI12/00265, PI12/01270, PI12/00715, PI12/00150), Fundación Marqués de Valdecilla (API 10/09), ICGC International Cancer Genome Consortium CLL, Junta de Castilla y León (LE22A10-2), Consejería de Salud of the Junta de Andalucía (PI-0571), Conselleria de Sanitat of the Generalitat Valenciana (AP_061/10), Recercaixa (2010ACUP 00310), Regional Government of the Basque Country by European Commission GrantsFOOD-CT-2006-036224-HIWATE, Spanish Association Against Cancer (AECC) Scientific Foundation and the Catalan Government DURSI Grant 2014SGR647S