Bacteria, viruses and parasites cause around 2m cases of cancer in the world each year, experts believe.

Of the 7.5m global deaths from cancer in 2008, an estimated 1.5m may have been due to potentially preventable or treatable infections.

Scientists carried out a statistical analysis of cancer incidence to calculate that around 16% of all cancers diagnosed in 2008 were infection-related. The proportion of cancers linked to infection was three times higher in developing countries than in developed ones.

Key cancer-causing infectious agents include human papillomavirus (HPV), the gastric bug Helicobacter pylori and the hepatitis B (HBV) and C viruses.

These four were together believed to be responsible for 1.9m cases of cancer, mostly gastric, liver and cervical cancers.

Cervical cancer accounted for around half of infection-related women's cancers. In men, more than 80% of infection-related cancers affected the liver, stomach and colon.

Dr Catherine de Martel and Dr Martyn Plummer, from the International Agency for Research on Cancer in Lyon, wrote in the Lancet Oncology journal: "Infections with certain viruses, bacteria, and parasites are one of the biggest and preventable causes of cancer worldwide … Application of existing public-health methods for infection prevention, such as vaccination, safer injection practice, or antimicrobial treatments, could have a substantial effect on future burden of cancer worldwide."

The researchers used information from a number of sources, including a cancer-incidence database covering 27 cancers from 184 countries.

Commenting on the findings, Dr Goodarz Danaei from the Harvard School of Public Medicine in Boston, wrote: "Their estimates show the potential for preventive and therapeutic programmes in less developed countries to significantly reduce the global burden of cancer and the vast disparities across regions and countries.

"Since effective and relatively low-cost vaccines for HPV and HBV are available, increasing coverage should be a priority for health systems in high-burden countries."