A review of data from more than 19 million people indicates that diabetes significantly raises a person’s risk of developing cancer.
When researchers compared patients with diabetes and without, both male and female diabetics had an increased risk of leukemias and lymphomas as well as certain solid tumors.
Researchers also found that diabetes conferred a higher cancer risk for women than men, both for all cancers combined and for some specific cancers, including leukemia.
“The link between diabetes and the risk of developing cancer is now firmly established,” said Toshiaki Ohkuma, PhD, of The George Institute for Global Health at the University of New South Wales in Australia.
“We have also demonstrated, for the first time, that women with diabetes are more likely to develop any form of cancer and have a significantly higher chance of developing kidney, oral, and stomach cancers and leukemia.”
Dr Ohkuma and his colleagues reported these findings in Diabetologia.
The researchers conducted a systematic search in PubMed MEDLINE to identify reports on the links between diabetes and cancer. Additional reports were identified from the reference lists of the relevant studies.
Only those cohort studies providing relative risks (RRs) for the association between diabetes and cancer for both women and men were included. In total, 107 relevant articles were identified, along with 36 cohorts of individual participant data.
RRs for cancer were obtained for patients with diabetes (types 1 and 2 combined) versus those without diabetes, for both men and women. The women-to-men ratios of these relative risk ratios (RRRs) were then calculated to determine the excess risk in women if present.
Data on all-site cancer was available from 47 studies, involving 121 cohorts and 19,239,302 individuals.
Diabetics vs non-diabetics
Women with diabetes had a 27% higher risk of all-site cancer compared to women without diabetes (RR=1.27; 95% CI 1.21, 1.32; P<0.001).
For men, the risk of all-site cancer was 19% higher among those with diabetes than those without (RR=1.19; 95% CI 1.13, 1.25; P<0.001).
There were several hematologic malignancies for which diabetics had an increased risk, as shown in the following table.
|Cancer type||RR for women (99% CI)||RR for men (99% CI)|
|Lymphatic and hematopoietic tissue||1.24 (1.05, 1.46)*||1.21 (0.98, 1.48)|
|Leukemia||1.53 (1.00, 2.33)||1.22 (0.80, 1.85)|
|Myeloid leukemia||0.83 (0.39, 1.76)||1.12 (0.77, 1.62)|
|Acute myeloid leukemia||1.33 (1.12, 1.57)*||1.14 (0.56, 2.33)|
|Chronic myeloid leukemia||1.67 (1.27, 2.20)*||1.62 (1.32, 1.98)*|
|Lymphoid leukemia||1.74 (0.31, 9.79)||1.20 (0.86, 1.68)|
|Lymphoma||2.31 (0.57, 9.30)||1.80 (0.68, 4.75)|
|Non-Hodgkin lymphoma||1.16 (1.02, 1.32)*||1.20 (1.08, 1.34)*|
|Hodgkin lymphoma||1.20 (0.61, 2.38)||1.36 (1.05, 1.77)*|
|Multiple myeloma||1.19 (0.97, 1.47)||1.12 (0.90, 1.41)|
|*denotes statistical significance with a P value < 0.01|
Calculation of the women-to-men ratio revealed that women with diabetes had a 6% greater excess risk of all-site cancer compared to men with diabetes (RRR=1.06; 95% CI 1.03, 1.09; P<0.001).
The women-to-men ratios also showed significantly higher risks for female diabetics for:
- Kidney cancer—RRR=1.11 (99% CI 1.04, 1.18; P<0.001)
- Oral cancer—RRR=1.13 (99% CI 1.00, 1.28; P=0.009)
- Stomach cancer—RRR=1.14 (99% CI 1.07, 1.22; P<0.001)
- Leukemia—RRR=1.15 (99% CI 1.02, 1.28; P=0.002).
However, women had a significantly lower risk of liver cancer (RRR=0.88; 99% CI 0.79, 0.99; P=0.005).
There are several possible reasons for the excess cancer risk observed in women, according to study author Sanne Peters, PhD, of The George Institute for Global Health at the University of Oxford in the UK.
For example, on average, women are in the pre-diabetic state of impaired glucose tolerance 2 years longer than men.
“Historically, we know that women are often under-treated when they first present with symptoms of diabetes, are less likely to receive intensive care, and are not taking the same levels of medications as men,” Dr Peters said. “All of these could go some way into explaining why women are at greater risk of developing cancer, but, without more research, we can’t be certain.”