Overall, women with diabetes were 28 per cent more likely to be diagnosed with more advanced and aggressive types of tumours than women without diabetes, the study found. Whether women with diabetes used insulin didn’t appear to influence the characteristics of their breast cancers.
“This finding matter for patients with type 2 diabetes who may be concerned about how insulin treatment may affect breast cancer risk,” said Christina Dieli-Conwright, a researcher at the University of Southern California in Los Angeles who wasn’t involved in the study.
Type 2 diabetes, the most common form, is linked to obesity and ageing and happens when the body can’t properly use or make enough of the hormone insulin to convert blood sugar into energy. Failure to manage the condition can result in complications like blindness, kidney failure, nerve damage and amputations.
Many people with type 2 diabetes can control their symptoms with prescription drugs designed to help lower blood sugar and with lifestyle modifications like eating healthier food and exercising more often. Some of these patients also need to inject insulin to help regulate their blood sugar.
Some previous research has linked insulin use to an increased risk of breast cancer in women with type 2 diabetes, but results have been mixed and often lacked detailed information about the exact types of tumours women developed, researchers note in Diabetes Care.
In the current study, women with diabetes were more likely to have more advanced tumours, which were larger and had spread to more lymph nodes surrounding the breast. With diabetes, women were also more likely to have tumours that were ‘graded’ as more aggressive and more likely to grow and spread rapidly in the body.
Beyond its small size, another limitation of the study is that it lacked data on a range of individual patient characteristics including obesity and any history of abnormal mammogram findings, note the authors, Jetty Overbeek of VU University Medical Center in Amsterdam and colleagues. Overbeek didn’t respond to requests for comment.
“Perhaps this study did not find insulin to play a role in breast cancer progression because of the small sample size,” she added. “This is an understudied area within diabetes and cancer risk, thus further larger studies are warranted to examine the impact of insulin treatment on cancer risk.”
In addition to taking prescribed medications and making lifestyle changes to lose weight, diabetics should also make sure to get regular screening mammograms and seek immediate medical attention when they detect pain or lumps in their breasts, Dr Chowdhury advised.