The risk of cancer is now thought to be heavily influenced by external factors such as smoking.

Risk heavily influenced by smoking, diet and alcohol

The risk of developing cancer is heavily influenced by external factors and not just down to bad luck, according to new research.

The study published in the journal Nature provides evidence that intrinsic risk factors contribute only modestly to cancer development (Around 10 - 30 per cent). 

It demonstrates that the correlation between stem-cell division and cancer risk does not distinguish between intrinsic and extrinsic factors.

Scientists say that the results are important for the future of cancer prevention, research and public health.

Cancers are thought to be caused by the malignant transformation of normal tissue and stem cells. This can be caused either by intrinsic factors - such as the risk of mutations occurring every time a cell divides, or extrinsic factors such as diet, alcohol and smoking.

In the study, a team of doctors from New York sought to explain the relative importance of these intrinsic and extrinsic factors. Using four methods, including computer modelling, population data and genetic approaches, the doctors found that the risk of cancer was due to extrinsic factors 70-90 per cent of the time.

"We have provided a new framework to quantify lifetime cancer risk from both intrinsic and extrinsic factors on the basis of four independent approaches that are data-driven and model-driven, with and without using the stem-cell estimations," the doctors say.

"Importantly, these four approaches provide a consistent estimate of contribution of extrinsic factors of 70-90 per cent in most common cancer types. This is consistent with the overall conclusion regarding the role of extrinsic factors in cancer development."

Image (C) Paolo Neo