DIABETES AND CANCER RISK

Men and women with type 2 diabetes had a 32% and 64% greater risk of developing cancer, respectively, compared with their peers in the general population, in a large study in Shanghai, China.

The researchers analyzed data from more than 400,000 adults with type 2 diabetes who had close to 8500 incident cancers during an average 3-year follow-up.

Men with type 2 diabetes were more likely to have 11 types of cancer than other men of the same age, whereas women with type 2 diabetes were more likely to have 13 types of cancer than other women of the same age.    

The findings imply that clinicians who treat type 2 diabetes may need to perform more physical examinations and pay closer attention to managing a patient's other risk factors for cancer, senior author Bin Cui, PhD, Shanghai Jiao Tong University, China, told Medscape Medical News in an email.

"We suggest that establishing strategies for regular cancer-specific screening and prevention care among patients with [type 2 diabetes] are necessary," the group concludes.

The study by Jiying Qi, a master's degree student at Shanghai Jiao Tong University, and colleagues was published online May 9 in the Journal of Diabetes.

Worldwide, an estimated 8.5% of the adult population (422 million people) have type 2 diabetes, and about a quarter of them (148 million; 10.9% of the population) live in China.

Meanwhile, cancer is the leading cause of death in China.

Only some previous studies have found that type 2 diabetes is associated with an increased risk of cancer.

It is important to clarify the risk of cancer among patients with diabetes, especially in China where so many have type 2 diabetes, yet there have been few published studies of the relationship between the diseases in this population.  

To investigate this, the authors obtained data from a centralized database from 60 hospitals in Shanghai, which was set up in 2013.

They identified 410,191 patients aged 20 to 99 years who had been treated for type 2 diabetes in these hospitals during July 2013 to December 2016.

They further identified the new incidence of 23 common types of cancer in these patients, with follow-up through December 2017. The patients were a mean age of 61.8 years and were followed for a mean 3.2 years. 

11 Types of Cancer in Men, 13 Types in Women

Among 204,080 men with type 2 diabetes, there were 4312 incident cases of cancer.

Men with type 2 diabetes had a significantly higher risk of prostate cancer(standardized incidence ratio [SIR], 1.86) compared with men in the general population.

Men with diabetes also had a significantly higher incidence of leukemia (SIR, 1.55), skin cancer (1.55), thyroid cancer (1.52), lymphoma (1.48), kidney cancer (1.45), liver cancer (1.39), pancreatic cancer (1.35), lung cancer (1.27), colorectal cancer (1.22), and stomach cancer (1.16) compared with their peers without diabetes.

On the other hand, men with type 2 diabetes had a significantly lower risk of esophageal cancer (SIR, 0.71).

Moreover, the risk of cancers of the nasopharynx, small intestine, gallbladder, larynx, bladder, or genital sites other than the prostate, were similar among men with or without type 2 diabetes. 

Among the 206,111 women with diabetes, there were 4173 incident cases of cancer.

Women with type 2 diabetes had a significantly higher incidence of cancer of the liver (SIR, 2.13), esophagus (2.07), thyroid (1.95), lung (1.84), and pancreas (1.61), as well as lymphoma (1.59), uterine cancer (1.58), colorectal cancer (1.51), leukemia (1.50), breast cancer (1.48), cervical cancer (1.38), or stomach cancer (1.30) compared with women without diabetes.

Women with type 2 diabetes also had a significantly higher risk of nasopharynx cancer (SIR, 2.33), although this type of cancer was very rare, occurring in only 15 women.

On the other hand, women with type 2 diabetes had a significantly decreased risk of gallbladder cancer (SIR, 0.77) compared with their peers in the general population.

And risks of cancer of the small intestine, larynx, skin, kidney, bladder, or ovary or other genital cancers were similar in women with or without diabetes.  

Future Studies Needed 

The findings of an increased risk of stomach, colorectal, liver, pancreatic, lung, and thyroid cancer, as well as lymphoma and leukemia in adults with type 2 diabetes are in line with results of previous studies.

For example, prior studies have also shown that women with type 2 diabetes have a higher risk of breast, cervical, and uterine cancer.

Similarly, the elevated rate of prostate cancer among men with diabetes has been seen in previous studies in China but contrasts with studies in Western populations.

"There may be differences in the exposure to risk factors, such as tobacco smoking, obesity, and genetic background, for populations from different geographical areas, which may also contribute to the inconsistent results," Qi and colleagues write.

The current study was not designed to consider obesity or body mass index as risk factors for cancer, Cui told Medscape Medical News.

However, because the current results were generally consistent with most past studies, "it is unlikely that these [confounders] explain the entire association between [type 2 diabetes] and cancer risk," the authors write. 

Nevertheless, "future studies are needed to distinguish the effects of [type 2 diabetes] from those of common risk factors," Qi and colleagues conclude.

The study was funded by grants from the National Key R&D Program of China, National Natural Science Foundation of China, Shanghai Municipal Education Commission-Gaofeng Clinical Medicine, and Shanghai Sailing Program.  

J Diabetes. Published online May 8, 2019. Abstract