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Diabetes increases breast cancer mortality risk

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January 22, 2018

Women with breast cancer and diabetes have a greater risk for all-cause and cancer-specific mortality and are less likely to receive chemotherapy and radiotherapy compared with women with breast cancer alone, according to researchers.

Iliana C. Lega, MD, MSc, of the Women’s College Research Institute at the University of Toronto, and colleagues evaluated data from Ontario administrative databases to compare the rate of receipt of breast cancer treatment between women with and without diabetes. Participants were diagnosed with breast cancer between 2007 and 2012. Those with diabetes and breast cancer (n = 4,955) had a diagnosis of diabetes at least 180 days before the cancer diagnosis and were matched to participants with breast cancer and no diabetes (n = 9,910). Forty-four percent of participants were diagnosed with breast cancer before age 65 years; mean age at diagnosis was 66.8 years.

Participants with diabetes and stage III breast cancer were less likely to receive chemotherapy than those with stage III breast cancer alone (RR = 0.93; 95% CI, 0.89-0.97); results were similar for participants with diabetes and any stage breast cancer compared with those with any stage breast cancer alone (RR = 0.93; 95% CI, 0.89-0.96). No differences were observed for receipt of chemotherapy after adjustment for cardiovascular disease, renal disease, dementia and weighted Johns Hopkins' Aggregated Diagnosis Group score.

Radiotherapy was less likely to be received by participants with diabetes treated with lumpectomy than those without diabetes (RR = 0.97; 95% CI, 0.95-0.99) and for participants with diabetes overall (RR = 0.93; 95% CI, 0.9-0.95).

All-cause (HR = 1.42; 95% CI, 1.3-1.55) and cancer-specific mortality (HR = 1.24; 95% CI, 1.05-1.46) were higher among participants with diabetes than those without diabetes; these results were not altered after adjustment for receipt of chemotherapy or radiotherapy.

Breast-cancer specific mortality was increased among participants with diabetes duration of more than 5 years (adjusted HR = 1.25; 95% CI, 1.02-1.54) and those with pre-existing CVD (aHR = 2.19; 95% CI, 1.09-4.42).

“These findings provide important prognostic information to direct counseling and treatment of women with both diabetes and breast cancer,” the researchers wrote. “Additional studies to identify factors that contribute to noncancer-related mortality in this group will help to minimize the differences in outcomes between women with and without diabetes.” – by Amber Cox

Disclosures: The authors report no relevant financial disclosures.