Nearly 6% of cancers, equating to almost 800,000 cases globally, were attributable to type 2 diabetes and overweight/obesity in 2012, new data show, with adiposity being responsible for almost twice as many cases as diabetes.
The study represents the first to estimate the worldwide cancer burden due to diabetes alone and also to diabetes and high body mass index (BMI) combined, say Jonathan Pearson-Stuttard, BMBCh, Imperial College London, United Kingdom, and colleagues in their paper published online November 28 in Lancet Diabetes & Endocrinology.
The new figures highlight the substantial role of diabetes in cancer worldwide, particularly in lower-income countries where rates of people being overweight and diabetes and cancer cases are soaring, they say.
“While obesity has been associated with cancer for some time, the link between diabetes and cancer has only been established quite recently,” stressed Dr Pearson-Stuttard.
“Our study shows that diabetes, either on its own or combined with being overweight, is responsible for hundreds of thousands of cancer cases each year across the world,” he noted in a press release from Imperial College.
He and his coauthors say that if global rates of diabetes and overweight continue to rise, the share of cancers attributable to the combined factors will increase by over 30% in women and by 20% in men by 2035.
“The distinct features of cancer patients are evolving throughout the world,” said Dr Pearson-Stuttard. “In the past, smoking was by far the major risk factor for cancer, but now healthcare professionals should also be aware that patients who have diabetes or are overweight also have an increased risk of cancer.”
Contribution of High BMI and Diabetes to 12 Cancers
Dr Pearson-Stuttard and colleagues estimated population-attributable fractions for 12 cancers by age and sex for 175 countries in 2012.
They selected cancers that the World Cancer Research Fund [WCRF] and the International Agency for Research on Cancer (IARC) have judged to have a causal association with high BMI (defined as >25 kg/m2): colorectal, gallbladder, pancreatic, liver, postmenopausal breast, endometrial, kidney, ovarian, stomach cardia, and thyroid cancer, esophageal adenocarcinoma, and multiple myeloma.
For the diabetes analysis, they included colorectal, gallbladder, pancreatic, liver, breast, and endometrial cancer.
Using comprehensive prevalence estimates of diabetes and BMI categories in 2002 and assuming a 10-year lag between exposure to diabetes or high BMI and incidence of cancer, combined with relative risks from published estimates, they quantified the contribution of diabetes and high BMI to site-specific cancers, individually and combined as independent risk factors and in a conservative scenario in which they assumed full overlap of risk of diabetes and high BMI.
They then used GLOBOCAN cancer incidence data to estimate the number of cancer cases attributable to the two risk factors.
Specifically, 5.6% of all incident cancers (792,600 cases) were attributable to the combined effects of diabetes and high BMI; individually, high BMI was responsible for 3.9% (544,300 cases) vs 2% (280,100 cases) for diabetes.
Variation by Cancer Site, Gender, and Geographic Region
The researchers found substantial variation in the proportion of cancer due to high BMI and diabetes by gender, by cancer site, and by geographical area.
Approximately one in four liver and esophageal adenocarcinomas and 38.4% of endometrial cancers worldwide in 2012 were estimated to be attributable to diabetes and high BMI.
Cancers caused by diabetes and being overweight or obese were almost twice as common in women as men (496,700 cases vs 295,900 in men).
In men, liver cancer was the commonest cancer caused by diabetes and high BMI, accounting for 126,700 cases, or 42.8% of all cancers caused by these two factors. Colorectal cancer was the second commonest, accounting for 63,200 new cancer cases, or 21.4%.
In women, breast cancer was the commonest cancer caused by diabetes and high BMI, accounting for 147,400 cases, or 29.7% of such cancers. Endometrial cancer was the second commonest, accounting for 121,700 new cancer cases, or 24.5%.
And the largest proportion of cancer cases attributable to the increase in prevalence of diabetes and high BMI during this period was in low-income and middle-income countries in Asia and sub-Saharan Africa.
This finding is key, “because these countries are generally less well equipped to manage the burden of complex noncommunicable diseases than high-income countries,” the authors note.
Underestimation of Cancer Burden Due to High BMI and Diabetes?
In an accompanying comment, Yikyung Park, MD, and Graham A Colditz, MD, both from Washington University School of Medicine, St Louis, Missouri, wonder whether the study might have underestimated the burden of cancer because the time lag between exposure and cancer was limited to 10 years, whereas there is emerging evidence that that high BMI in late adolescence/young adulthood is directly related to risk of cancer in old age.
“A focus on adiposity in midlife or later and insufficient consideration of lifetime adiposity could lead to substantial underestimation of the contribution of high BMI to the global burden of cancers,” they note.
“Both obesity and diabetes are preventable causes of cancer for which intervention is possible at multiple levels — in individuals, communities, healthcare systems, and policy.”
More prompt actions are needed to help people maintain a healthy body weight “throughout the life course, starting at an early age,” they conclude.
Also commenting on the new findings, American Society of Clinical Oncology (ASCO) CEO Clifford Hudis, MD, FACP, FASCO, said they “add another reason for the general public to be concerned about the health risks associated with obesity, which clearly include cancer.”
A recent survey by ASCO found that fewer than one in three people realize obesity is a risk factor for cancer, even though it is the second leading preventable cause of the disease.
“Armed with this increasing recognition of its medical risks, we must work together across medical disciplines to help…address this challenge,” he stressed.
Senior author Majid Ezzati reports a charitable grant from the Young Health Programme of AstraZeneca and personal fees from Third Bridge, Scor, and Prudential outside the submitted work. All other authors declare no relevant financial relationships, as do the editorialists.
Lancet Diabetes Endocrinol. Published online November 28, 2017. Article, Editorial
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