PARIS (AFP) - Being overweight and obesity are now causing nearly half a million new cancer cases in adults every year, roughly 3.6 per cent of the world's total, a study said on Wednesday.
A quarter of these cases are "realistically avoidable", said the authors of the work published in The Lancet Oncology.
Led by scientists at the International Agency for Research on Cancer, the paper drew on a range of sources, including a large database of cancer incidence and mortality for 184 countries in 2012.
In men, being overweight was blamed for 136,000 new cases, more than two-thirds of them cancers of the colon and kidney.
In women, it was linked to 345,000 cancer diagnoses, nearly three-quarters of which were post-menopausal breast, endometrial and colon cancers.
Mirroring the spread of obesity in developed countries, the tally was highest in North America, which accounted for nearly a quarter of all the weight-related new cancer cases.
Sub-Saharan Africa had the fewest, with 7,300 cases.
"Our findings add support for a global effort to address the rising trends in obesity," said lead researcher Melina Arnold.
"The global prevalence in adults has doubled since 1980. If this trend continues, it will certainly boost the future burden of cancer, particularly in South America and North Africa, where the largest increases in the rate of obesity have been seen over the last 30 years."
Measured as a ratio of weight in kg-to-height in metres squared, a body mass index (BMI) of 25 to 29.9 is considered overweight, and 30 plus as obese.
Elsewhere in The Lancet, an updated map of cancer survival shed light on a persisting gulf between rich and poor countries, as well as within advanced economies themselves.
The Concord-2 study looked at a key benchmark - the rate for survival five years after diagnosis - among 25.7 million patients who had had one of 10 common cancers.
For acute lymphoblastic leukaemia in children - the most common childhood cancer - the rate ranged from 90 per cent in Canada, Austria, Belgium, Germany and Norway, to just 16-50 per cent in Jordan, Lesotho, central Tunisia, the Indonesian capital Jakarta and Mongolia.
In most developed countries as well as in Brazil, Colombia and Ecuador, the five-year survival from breast and colorectal cancers has increased, thanks to earlier diagnosis and better treatment.
There remains a major gap in the survival rate of cervical and ovarian cancers.
Five-year survival for these two types of cancer varies from more than 70 per cent in Mauritius, South Korea, Taiwan, Iceland and Norway to less than 40 per cent in Libya.
Within Europe, cervical and ovarian cancer survival is 60 per cent or less in Britain, France, Ireland, Bulgaria, Latvia, Poland, Russia and Slovakia.
The study should be a barometer for national health policy, said Dr Claudia Allemani at the London School of Hygiene and Tropical Medicine.
"In some countries, cancer is far more lethal than in others - in the 21st century, there should not be such a dramatic gulf in survival."