For men, obesity and diabetes accounted for a more than 40 per cent of liver cancers, while for women they were responsible for a third of uterine cancers, and nearly as many cases of breast cancer, researchers said.
"While obesity has been associated with cancer for some time, the link between diabetes and cancer has only been established quite recently," said Jonathan Pearson-Stuttard, from Imperial College London in the UK.
"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," Pearson-Stuttard said, lead author of the study published in the journal The Lancet Diabetes and Endocrinology.
The global increase in diabetes between 1980 and 2002 accounted for a quarter of the eight lakh cases, while the obesity epidemic over the same period resulted in an additional 30 per cent of cases.
On current trends, the share of cancers attributable to the two conditions will increase by 30 per cent for women and 20 per cent for men in less than 20 years, the researchers warned.
"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," Pearson-Stuttard said.