The risk for developing a “more aggressive” form of breast cancer is higher among women with type 2 diabetes compared with women without diabetes, according to findings published in Diabetes Care.
Use of insulin analogues did not increase risk for more aggressive breast cancers, according to researchers.
“Several mechanisms have been suggested for the increased risk of breast cancer among women with [type 2 diabetes],” Jetty A. Overbeek, MSc, of the department of general practice and elderly care medicine in the Amsterdam Public Health Research Institute at VU University Medical Centre in Amsterdam, and colleagues wrote. “It is yet unclear what the pathophysiologic interactions between diabetes and breast cancer are and whether improvements in diabetes care can reduce the increased mortality in patients with breast cancer.”
Overbeek and colleagues conducted a nested case-control study based on data from the Netherlands Cancer Registry and PHARMO Database Network. The registry was used to establish cancer diagnosis while the database network was used to establish the presence of type 2 diabetes, which was defined by the receipt of two or more noninsulin blood glucose-lowering drugs within 6 months. Women with type 2 diabetes for at least 4 years before cancer diagnosis were included (n = 1,567; mean age, 71 years). The type 2 diabetes group was matched with 6,267 women without diabetes (mean age, 71 years) and separately divided into cohorts based on insulin use (n = 388) and nonuse (n = 1,179).
The researchers found that tumors were larger among women with type 2 diabetes compared with women without type 2 diabetes (P < .01). In addition, women with type 2 diabetes had more lymph nodes affected (P < .05), a more advanced tumor stage (P < .01) and grade (P < .05) and less frequent instances of a progesterone receptor-negative breast tumor (P < .0001) than women without type 2 diabetes. The significance of these findings for tumor size (OR = 1.22; 95% CI, 1.08-1.38), lymph nodes affected (OR = 1.31; 95% CI, 1.12-1.53), tumor stage (OR = 1.28; 95% CI, 1.13-1.44), tumor grade (OR = 1.22; 95% CI, 1.08-1.39) and progesterone receptor-negative breast tumor (OR = 0.77; 95% CI, 0.67-0.89) held after adjusting for age, year of cancer diagnosis, socioeconomic status, chronic disease score and the use of glucocorticoids, estrogen-progestogen contraceptives and hormone therapy.
In comparing the use of insulin vs. nonuse, the researchers did not find a significant association with breast cancer characteristics.
“Based on the current data, we see no reason to restrain the use of insulin (analogue) among women with [type 2 diabetes] with regard to its effects on breast cancer subtype and expected subsequent prognosis,” the researchers wrote. – by Phil Neuffer
Disclosure: Overbeek reports she is an employee of the PHARMO Institute for Drug Outcomes Research.