Diabetes can increase the risk of developing a number of cancers and may reduce the chances of survival in cancer patients, a study has found. Researchers from the Swedish National Diabetes Register (NDR) compared over 450,000 people with type 2 diabetes with more than 2 million matched controls over an average of 7 years. For the most common cancers, individuals with diabetes face a 20 percent greater risk of developing colorectal cancer and a five percent higher risk of breast cancer compared with their diabetes-free counterparts.
People with diabetes already diagnosed with cancer also fare worse, with a 25 percent and 29 percent higher chance of dying following a breast and prostate cancer diagnosis respectively than their peers without diabetes. More than 415 million people are living with diabetes worldwide — equivalent to 1 in 11 of the adult population — and this figure is expected to rise to 642 million by 2040.
Previous research has suggested a link between type 2 diabetes and an increased risk of cancer. However, the relationship between diabetes and cancer remains poorly understood due to limitations of previous studies. To provide more evidence, researchers examined the incidence of a number of cancers and post-cancer mortality in 457,473 individuals with type 2 diabetes from the NDR between 1998 and 2014, compared to 2,287,365 controls from the general population over an average of 7 years follow up.
A total of 227,505 people developed cancer over the follow-up period. Diabetes was associated with 11 out of the 12 specific types of cancer investigated in the study. Scientists found that people with diabetes were 231 percent more likely to be diagnosed with liver cancer than those without a history of diabetes over the study period. Diabetes was also clearly linked with higher risk of cancers of the liver, pancreas (119 per cent), uterus (78 per cent), penis (56 per cent), kidney (45 per cent), gallbladder and bile ducts (32 per cent), stomach (21 per cent), and bladder (20 per cent).
There was evidence that those with diabetes were at a reduced risk of prostate cancer (18 percent) compared to their peers without diabetes. The absolute 5-year risk of developing cancer for the cancer sites highlighted in the study ranged from 0.02 percent for penis cancer to 1.45 percent for prostate cancer for people with diabetes.
In addition, for individuals with diabetes, mortality was higher for prostate (29 percent higher), breast (25 percent), and colon (9 percent) cancer compared to their diabetes-free counterparts. The researchers emphasise that although the relative risk of cancer is increased after diabetes, the absolute risk increase is low.
“Our findings do not suggest that everyone who has diabetes will go on to develop cancer in later life,” said Bjornsdottir, who led the study. “With the number of people with type 2 diabetes doubling over the past 30 years our findings underscore the importance of improving diabetes care,” she said.