About 5 percent of all cancers in South Africa are due to unknown causes. Tobacco use accounts for almost a third of all cases

A study, published in the journal Science at the beginning of the year, suggested that two-thirds of cancers were caused by chance and therefore could not be prevented.

But international cancer bodies and scientists have slammed the report, saying it is misleading and potentially harmful as it may deter people from making lifestyle choices proven to prevent cancer.

Dr Carl Albrecht, head of research for the Cancer Association of South Africa (CANSA) said numerous studies clearly show the impact of environmental and lifestyle factors on the different types of cancer affecting different populations.

“The past five decades of international epidemiological research have shown that most cancers that are frequent in one population are relatively rare in another and that these patterns vary over time,” according to the International Agency for Research on Cancer (IARC), the World Health Organisation’s specialised cancer agency.

“For example, oesophageal cancer is common among men in East Africa but rare in West Africa… these observations are characteristic of many common cancers and are consistent with a major contribution of environmental and lifestyle exposures, as opposed to chance,” said the IARC, which also rejected the “bad luck” report findings.

The controversial article by researchers from the US Johns Hopkins University in Baltimore studied the stem cell division (a natural process of cell renewal) of tissue samples from 31 areas in the body, for example, oesophagus, stomach, bone, brain, etc. Two-thirds of the tissue showed high rates of division and random mutations (irregular cell division that may lead to the formation of cancerous cells) leading the researchers to conclude that the same ratio of cancers occur randomly, or as they described it, due to “bad luck”.

But IARC argues that the study omitted tissue from body regions most commonly affected by cancer, such as the breast, cervix and prostate, while emphasizing rare types such as bone and brain cancers. The results – that looked at a small sample that was not representative of the disease profile in actual human populations – could therefore not be applied to cancer in general.

IARC does not dispute the fact that the number of cell division increases the risk of cancer, but maintains that most cancers occurring worldwide are strongly related to environmental and lifestyle exposure. “Therefore, these cancers are preventable; based on current knowledge, nearly half all cancers worldwide can be prevented,” reads IARC’s report.

Albrecht reiterates this. “CANSA will not be changing its philosophy that 90 percent of cancers are caused by environmental carcinogens and lifestyle. Chance may be involved in less than 10 percent of cancers being diagnosed, but that remains to be seen,” says Albrecht. – Health-e News.

• Read more on what causes cancer in South Africa