Cancer Risk Increased Before, After Diabetes Diagnosis

A new study has found an increased risk for a cancer diagnosis during the 10 years prior to and the 3 months immediately after being diagnosed with type 2 diabetes. The study was published online in Cancer.

“These findings suggest that the relationship between diabetes and cancer can be explained in part by detection bias, whereby there is enhanced detection of cancers within the setting of increased healthcare around a diabetes diagnosis,” wrote researcher Iliana Lega, MD, MSc, of the University of Toronto, and colleagues. “Although further research is needed to confirm these findings, enhanced cancer screening and cancer prevention strategies in patients with and at risk of developing diabetes may be warranted.”

These findings came from a retrospective, population-based cohort study of more than 1 million adults living in Ontario, Canada. Lega and colleagues used data from administrative healthcare databases to identify patients with new diagnosis of diabetes between April 1997 and March 2007 and matched them with people without diabetes. They then linked these data with the Ontario Cancer Registry to identify individuals with incident cancer diagnosis. They examined cancer diagnosis for three periods: within the 10 years prior to diabetes diagnosis, within the first 3 months after diagnosis, and from 3 months to 10 years after diagnosis.

Patients diagnosed with diabetes were significantly more likely to have been diagnosed with cancer within the 10 years prior to the diabetes diagnosis compared with individuals without diabetes (hazard ratio [HR], 1.23 [95% CI, 1.19–1.27]). In addition, the incidence of prior cancer was higher for patients with diabetes at each individual cancer site studied except for ovarian and cervical cancer.

“This finding is consistent with other studies that have shown a significantly higher rate of breast cancer and colon cancer before a diagnosis of diabetes,” the researchers wrote. “This observation may be due to shared metabolic risk factors for diabetes and cancer that are present during the prediabetes period, such as insulin resistance and hyperinsulinemia.”

In the 3 months immediately after the diabetes diagnosis, incidence of any cancer was 19.3 per 1,000 person years in people with diabetes compared with 10.6 per 1,000 person years for those without diabetes. The rate of cancer diagnosis was 62% higher in patients with diabetes compared with those without diabetes (HR, 1.62 [95% CI, 1.52–1.74]). No increased risk for cancer was found from 3 months to 10 years post-diagnosis.

“These findings support the possibility that epidemiologic associations between diabetes and cancer can be partially explained by a detection bias around the time of a diabetes diagnosis, when there is greater healthcare contact,” the researchers wrote. “The current study findings also suggest that individuals with diabetes have a higher risk of cancer even before a diagnosis of diabetes. The results of the current study have important implications for our understanding of the complex relationship between these conditions, and may help to inform the design of future studies and the counseling of patients regarding their risk of cancer.”