The study, published in May 2019 in the Journal of Diabetes, follows several other studies over the past decade — including an Australian study published in February 2015 in the journal Diabetes Care, a Swedish study published in January 2015 in the International Journal of Cancer, and previous research from Japan — that have pointed to a convincing association between diabetes and cancer, says coauthor Bin Cui, MD, of the Shanghai Jiao Tong University School of Medicine in China. “This study was not the first one to detect the relationship between type 2 diabetes and an increased risk of cancer,” Dr. Cui says. “Previous studies have mostly reported an increased risk of total cancers among patients with diabetes. The association between diabetes and cancer risk depends on the specific cancer site.” The new report provides a closer look at those specific risks. Cui and his colleagues examined the health of 410,191 adults in mainland China with type 2 diabetes who didn’t have cancer at the beginning of the investigation. Study authors followed participants from July 2013 to December 2016 and assessed whether they developed cancer. The authors then compared these cancer rates to those in the general population. Researchers found men with diabetes had a 34 percent increased risk of developing cancer, while women with diabetes had a 62 percent increased risk. The higher risks were linked with a range of cancer types. Men had a significantly higher risk — almost double — for prostate cancer. But type 2 diabetes was also linked with higher risks of leukemia, skin cancer, thyroid cancer, lymphoma, kidney cancer, liver cancer, pancreatic cancer, lung cancer, colorectal cancer, and stomach cancer. Men with diabetes had a lower risk for esophageal cancer. Women with type 2 diabetes had a twofold higher risk of nasopharynx cancer. They also had elevated risks for liver cancer, esophageal cancer, thyroid cancer, lung cancer, pancreatic cancer, lymphoma, uterine cancer, colorectal cancer, leukemia, breast cancer, cervical cancer, and stomach cancer. Yet women had a lower risk for gallbladder cancer. RELATED: Obesity Triggering Rising Cancer Rates in Millennials, Study Suggests
Comparing the New Study Findings to Past Research on Diabetes and Cancer
While some of the findings were consistent with previous studies, Cui says, a few differences stood out. “This study showed a significant positive association between type 2 diabetes and prostate cancer risk, which was consistent with some studies carried out in China but inconsistent with studies among Western populations,” Cui says. For example, a study published in February 2015 in the journal Diabetes Care found a decreased risk of prostate cancer in U.S. men with diabetes. “There is no question that certain cancers are more common in diabetes patients, particularly when diabetes is associated with obesity,” says Joel Zonszein, MD, director of the diabetes center at the University Hospital of the Albert Einstein College of Medicine in New York City and a member of the Endocrine Society. Dr. Zonszein was not involved in the study. “The advantage of this study in China is that it shows there are some discrepancies between other studies. That is important because genetic anomalies between races differ.” Scientists have recognized the overall relationship between cancer and diabetes for many years. In 2010, a joint committee of the American Diabetes Association (ADA) and American Cancer Society released a consensus report identifying the higher cancer risks faced by people with diabetes. The report delved into possible explanations for the elevated risk. For example, the authors of that report noted, the diseases share some risk factors. Obesity, which is common among people with type 2 diabetes, also elevates cancer risk. And, according to the American Diabetes Association, the risk of both diabetes and cancer is higher among people who smoke and among African Americans. There is also some evidence that higher levels of insulin circulating in the blood boost the risk, noted a review published in CA: A Cancer Journal for Clinicians. “There is a lot of speculation on what the mechanisms might be,” that increase cancer risk, says Victor R. Lavis, MD, a professor in the department of endocrine neoplasia and hormonal disorders at The University of Texas MD Anderson Cancer Center in Houston, and a member of the Endocrine Society. Dr. Lavis was not involved in the study. “A major driver of the association is obesity. Obese people tend to have higher insulin levels, as do people with type 2 diabetes. And insulin tends to promote cell growth and division, which are characteristics of cancer in some ways.” RELATED: What Are the Possible Complications of Type 2 Diabetes?
Reducing Your Risk for Cancer and Type 2 Diabetes by Managing Weight and Blood Sugar
The two diseases share some risk-reduction strategies, the experts point out. Numerous studies have found that exercise, losing weight, and eating a healthy diet can help lower your risk for both diseases, the ADA points out. “We can treat obesity with lifestyle modifications,” Zonszein says. “We have drugs to bring down blood sugar levels and lower the obesity risk. We have to treat that — that’s number one.” RELATED: 9 Steps Proven to Help Lower Your BMI Physicians and patients need to pay attention to the higher incidence of cancer in people with diabetes and make sure patients adhere to a regular schedule of cancer screenings, Cui says. But people with diabetes may be under-screened for cancer, Lavis says. “There is some evidence that people with diabetes get less screening, on average, and they should probably get at least as much,” he says. “You should not neglect your mammogram because you are treated for diabetes.” People with diabetes who see a primary care doctor on a regular basis may be more likely to discuss and receive regular cancer screenings, he suggests, compared with when patients only see a diabetes care specialist. Both patients and physicians should also remember the increased cancer risk when faced with new or unusual symptoms, Zonszein says. “The message is that these patients are at higher risk for cancer, and we should be alert,” he says. “When someone has been losing a lot of weight or has a lack of appetite, we should always look for cancer. That may be the presenting sign.” RELATED: What Are the Risk Factors for Cancer, and Can You Prevent It?
