Most cancer down to lifestyle choices, not ‘bad luck’

A leading cancer research organisation has hit out at a recent study which attributes cancer to ‘bad luck’.

The International Agency for Research on Cancer (IARC) said it “strongly disagrees” with the conclusion of the report on the causes of human cancer published earlier this month in the journal Science.

The research, which received widespread media coverage at the time, compared the number of lifetime stem cell divisions with lifetime cancer risks and suggested that random mutations, or bad luck, are “the major contributors to cancer overall, often more important than either hereditary or external environmental factors”.

The IARC, the World Health Organisation’s specialised cancer agency, raised a number of concerns with the study and said while it has long been known the number of cell divisions increases risk of mutations and, therefore, of cancer, most cancers are linked to environmental and lifestyle exposures.

Experts at the institution also pointed to serious contradictions with the extensive body of epidemiological evidence as well as a number of methodological limitations and biases in the analysis presented in the report.

According to the IARC, the report emphasises rare cancers like osteosarcoma and medulloblastoma and excludes common cancers such as those of the stomach, cervix, and breast.

In addition, the study focuses exclusively on the US population as a measure of lifetime risk. The IARC says that a comparison of different populations would have yielded different results.

Director of the IARC, Dr Christopher Wild, said the report could be easily misinterpreted, leading to negative consequences in terms of both cancer research efforts and public health perspectives.

“Concluding that ‘bad luck’ is the major cause of cancer would be misleading and may detract from efforts to identify the causes of the disease and effectively prevent it,” said Dr Wild.

“We already knew that for an individual to develop a certain cancer there is an element of chance, yet this has little to say about the level of cancer risk in a population.”

For the past five decades, research has shown most cancers that are frequent in one population are relatively rare in another and that these patterns very over time.

For example, oesophageal cancer is common among men in East Africa but rare in West Africa. Colorectal cancer, once rare in Japan, increased 400% in just 20 years.

The IARC says that these observations are characteristic of many common cancers and are consistent with a major contribution of environmental and lifestyle exposures, as opposed to genetic variation or chance.


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