The overall risk of a cancer diagnosis was more than three times higher in the first 3 months. It remained significantly elevated, though less so, in the first 5 years (HR, 1.5), and then fell off.
When the individual cancers were considered, only pancreatic cancer was significantly more common among the diabetes patients, and was almost 29 times more likely to be diagnosed in the first 3 months. However, Dr. De Bruijn noted, it’s tough to tease out that particular relationship, since the obesity that accompanies type 2 diabetes can also drive the development of pancreatic cancer.
Ellena Badrick, a researcher at the University of Manchester (England), also examined the idea of detection bias in a population database, exploring the time-dependent relationships for obesity-related cancers, compared with those not related to obesity.
She found 10,315 patients who were diagnosed with type 2 diabetes from 1995 to 2010. These were compared with 20,630 controls chosen from the same period. Obesity-related cancers were considered to be breast, endometrial, ovarian, renal, esophageal, pancreatic, and gallbladder.
There were 1,349 cancers among the patients with diabetes, of which 323 were related to obesity. Among the controls, there were 3,218 cancers, of which 634 were obesity related.
She also split her follow-up period into epochs since diabetes diagnosis: up to 6 months, 6-12 months, 12-24 months, 24 months-5 years, and beyond. Cancer incidence was reported as cases per 1,000 person/epoch.
There was a much higher detection rate overall in the first 6 months after diagnosis – more than 100 cases per 1,000 person-epoch. After 6 months, this dropped to less than 20 cases per 1,000 person-epoch. The incidence did increase over the follow-up period, but she said that reflected the expected age-related pattern.
The same pattern emerged when looking at obesity- vs. non–obesity-related cancers. In the first 6 months, the incidence of obesity-related cancer hovered around 30 per 1,000 person-epoch. By 1 year this had dropped to near zero. For non–obesity-related cancers, the incidence rate was much higher in the first 6 months, at nearly 80 per person/epoch. But this also dropped to near zero by 1 year. Both incidence curves followed the same slow increase as the subjects aged.
Over the entire follow-up, 27% of all the obesity-related cancers and 73% of the non–obesity-related cancers were diagnosed within the first year after a diagnosis of type 2 diabetes.
When cancers diagnosed during the first 2 years were excluded, patients with type 2 diabetes had a 43% increase in the risk of developing an obesity-related cancer during the study. There was no increased risk, however, in developing a cancer not related to obesity.
“This suggests that in patients with type 2 diabetes, cancer risk-reduction strategies should be targeted against obesity-related cancers,” Ms. Badrick said.
Mr. Carstensen is an employee of the Steno Diabetes Center, which is owned by Novo Nordisk. He disclosed that he owns stock in the company. Dr. De Bruijn and Ms. Badrick had no financial disclosures.