The study suggests that women using the common type 2 diabetes treatment, which helps to lower blood glucose levels, were 40 per cent less likely to have dense breast tissue, which is one of the most common tumour risk factors.
The findings, which were carried out by the University of Copenhagen, were unveiled at the European Breast Cancer Conference. The researchers say this is the first study investigating the impact of diabetes treatments on breast density.
A total of 5,644 women with an average age of 56 took part in the Danish Diet, Cancer and Health (DCH) study group. Each participant had attended mammographic screenings between 1993 and 2001.
The Copenhagen study team discovered that those who controlled their condition by diet or medication were far less likely to have dense breasts, but those who used insulin regularly were twice as likely to have high breast density.
Currently mammograms are the best way to detect early breast cancer but high density breast tissue can make the disease harder to find during the screenings.
Increased risk of breast cancer
Dr. Zorana Jovanovic Andersen, of the University of Southern Denmark, said: “Diabetes is associated with an increased risk of breast cancer, but the exact mechanisms which bring this about are still unclear.
“One of the characteristics of cancer cells is their ability to grow rapidly and uncontrollably, and to resist the programmed death that occurs in non-cancer cells. Therefore, growth factors are critical to cancer development and progression.
“We know that insulin is an important growth factor for all body tissues, and even if we do not know exactly how it affects the development of cancer cells, it is also highly plausible that it increases breast density.”
Andersen said more research was needed to further investigate the links between breast density and other risk factors for the disease.
She added: “In the meantime, we would urge all women, both with diabetes and without, to take measures to reduce their risk of developing breast cancer through simple lifestyle changes, such as avoiding obesity, reducing alcohol consumption and exercising.”
Chair of the conference, Professor Fatima Cardoso, director of the breast unit of the Champalimaud Clinical Centre in Lisbon, Portugal, said: “There has been much research into the role of the insulin pathway in breast cancer, but the exact mechanisms are still unknown.
“This study shows clearly that a link between diabetes treatment and breast density, an important risk factor for the disease, has been made. I hope that these findings will lead to further research into the effect of cheap, easily-available drugs such as metformin, not just on breast density, but on breast cancer risk overall.”
One in eight women will develop breast cancer over their lifetime. Recovery rates are good if it is detected early which is why the NHS advises women check their breasts regularly for any changes such as dimples, lumps and puckering.