The influence of diabetes severity on receipt of guideline-concordant treatment for breast cancer.

Diabetes severity may influence breast cancer treatment choices. We examined whether receipt of guideline-concordant breast cancer treatment varied with diabetes severity. Cancer registry data from seven states regarding 6,912 stage I-III breast cancers were supplemented by medical record abstraction and physician verification. We used logistic regression models to examine associations of diabetes severity with guideline-concordant locoregional treatment, adjuvant chemotherapy, and hormonal therapy adjusted for sociodemographics, comorbidity, and tumor characteristics. We defined guideline concordance using National Comprehensive Cancer Network guidelines, and diabetes and comorbidities using the Adult Comorbidity Evaluation-27 index. After adjustment, there was significant interaction of diabetes severity with age for locoregional treatment (p = 0.001), with many diabetic women under age 70 less frequently receiving guideline-concordant treatment than non-diabetic women. Among similarly aged women, guideline concordance was lower for women with mild diabetes in their late fifties through mid-sixties, and with moderate/severe diabetes in their late forties to early sixties. Among women in their mid-seventies to early eighties, moderate/severe diabetes was associated with increased guideline concordance. For adjuvant chemotherapy, moderate/severe diabetes was less frequently associated with guideline concordance than no diabetes [OR 0.58 (95 % CI 0.36-0.94)]. Diabetes was not associated with guideline-concordant hormonal treatment (p = 0.929). Some diabetic women were less likely to receive guideline-concordant treatment for stage I-III breast cancer than non-diabetic women. Diabetes severity was associated with lower guideline concordance for locoregional treatment among middle-aged women, and lower guideline concordance for adjuvant chemotherapy. Differences were not explained by comorbidity and may contribute to potentially worse breast cancer outcomes.