Two weeks ago, actress Angelina Jolie announced that she had undergone a preventive double mastectomy, a choice she made after finding out she carries a rare gene that raises a woman’s risk of developing breast cancer to about 65%. This revelation sparked a flurry of media coverage, which touched on everything from the cost of genetic testing to cultural factors that may influence whether a woman chooses to undergo a mastectomy. Suddenly, it seemed, breast cancer was on everyone’s mind. So it seemed like an opportune time for Diabetes Flashpoints to discuss the link between diabetes and breast cancer, as well as other types of cancer.
If hearing about that link comes as a surprise, you’re not alone; many people with diabetes are never told about the connection between diabetes and cancer. So just what is that connection? According to an analysis of 16 studies published in 2011 in the Asian Pacific Journal of Cancer Prevention, women with diabetes are 23% more likely than other women to develop breast cancer, especially after menopause, and 44% more likely to die of it. For reasons that are not clear, women with diabetes in Europe are more likely than those in America or Asia to develop breast cancer, with a risk 88% higher than the general population versus 16% in America and 1% in Asia.
Having diabetes also raises the risk of developing other cancers, but to varying degrees. According to an article published last year in Diabetes Forecast, people with diabetes are about twice as likely as those without diabetes to develop liver, pancreatic, or endometrial cancer. The risk of colorectal, bladder, and breast cancers is elevated but to a lesser and varying degree. Most other cancers show no statistical relationship with diabetes — with the exception of prostate cancer, which men with diabetes are actually less likely to develop. One expert quoted in the article, an endocrinologist at Mount Sinai Medical Center in New York City, noted that the evidence of a cancer connection is much stronger for Type 2 diabetes than for Type 1, since few studies have looked at people with Type 1 diabetes separately.
So what might explain the connection between diabetes and cancer? Some experts believe that elevated insulin levels are the most likely reason for the higher cancer risk, although this has yet to be proven. According to this theory, insulin may act as a growth factor for tumors, helping them grow while discouraging the death of cancer cells. People with diabetes who take injected or infused insulin are not the only ones whose insulin levels may be elevated. Most people with Type 2 diabetes, in fact, are likely to have higher levels of insulin than a person without diabetes would have due to the effects of insulin resistance. People with Type 1 diabetes, on the other hand, may have close to normal levels of insulin even though all of it is injected, especially if they also take the drug pramlintide (brand name Symlin), which mimics the natural hormone amylin and boosts the effects of insulin.
Were you already aware of the link between diabetes and cancer? If so, have you taken advantage of recommended screening tests for cancer, such as mammograms and colonoscopies? Or does diabetes already take too much mental energy for you to worry about cancer screening and prevention? Is there any benefit, in your view, in publicizing the diabetes–cancer connection? Leave a comment below!