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Most cancer types 'just bad luck'

By James Gallagher Health editor, BBC News website

Most types of cancer can be put down to bad luck rather than risk factors such

as smoking, a study has suggested.

A US team were trying to explain why some tissues were millions of times more

vulnerable to cancer than others.

The results, in the journal Science, showed two thirds of the cancer types

analysed were caused just by chance mutations rather than lifestyle.

However some of the most common and deadly cancers are still heavily influenced

by lifestyle.

And Cancer Research UK said a healthy lifestyle would still heavily stack the

odds in a person's favour.

So is it time to light-up, drink and eat what you want without a care in the

world?

It won't come as a surprise that the answer is no.

All cancer has an element of chance - a roll of the dice that decides whether

your DNA acquires a mutation that leads to cancer.

The study shows that two thirds of cancer types are simply chance.

But the remaining third are still heavily influenced by the choices we make.

Too much booze, time in the sun or being overweight mean we are playing with

loaded dice and the odds are not in our favour.

Remember smoking accounts for a fifth of all cancers worldwide.

These findings are a reminder that cancer is often just bad luck and the only

option is early detection.

But that's not an excuse to give up on those new year's resolutions already.

Grey line

In the US, 6.9% of people develop lung cancer, 0.6% brain cancer and 0.00072%

get tumours in their laryngeal (voice box) cartilage at some point in their

lifetime.

Toxins from cigarette smoke could explain why lung cancer is more common.

But the digestive system is exposed to more environmental toxins than the

brain, yet brain tumours are three times as common as those in the small

intestine.

Root of cancer

The team at Johns Hopkins University School of Medicine and Bloomberg School of

Public Health believe the way tissues regenerate is the answer.

Old tired cells in the body are constantly being replaced with new ones made by

dividing stem cells.

But with each division comes the risk of a dangerous mutation that moves the

stem cell one step closer to being cancerous.

The pace of turnover varies throughout the body with rapid turnover in the

lining of the gut and a slower pace in the brain.

Bone cancer

The researchers compared how often stem cells divided in 31 tissues in the body

over a lifetime with the odds of a cancer in those tissues.

They concluded that two thirds of cancer types were "due to bad luck" from

dividing stem cells picking up mutations that could not be prevented.

These cancer types included Glioblastoma (brain cancers), small intestine

cancers and pancreatic cancers.

Cristian Tomasetti, an assistant professor of oncology and one of the

researchers, said a focus on prevention would not prevent such cancers.

"If two thirds of cancer incidence across tissues is explained by random DNA

mutations that occur when stem cells divide, then changing our lifestyle and

habits will be a huge help in preventing certain cancers, but this may not be

as effective for a variety of others.

"We should focus more resources on finding ways to detect such cancers at

early, curable stages."

Poor lifestyle

Burger

The remaining third of cancer types, which are affected by lifestyle factors,

viruses or a heightened family risk, include some of the most common:

Basal cell carcinoma - a type of skin cancer made more common by too much UV

exposure

Lung cancer - strongly linked to smoking

Colon cancer - increased by poor diet and family risk genes

Two common types of cancer - breast and prostate - were not analysed as the

researchers could not find a consistent rate of stem cell division in those

tissues.

Separate research by Cancer Research UK shows more than four in 10 of the total

number of cancers were down to lifestyle.

Dr Emma Smith, senior science information officer at the charity, told the BBC:

"We estimate that more than four in 10 cancers could be prevented by lifestyle

changes, like not smoking, keeping a healthy weight, eating a healthy diet and

cutting back on alcohol.

"Making these changes is not a guarantee against cancer, but it stacks the odds

in our favour.

"It's vital that we continue making progress to detect cancer earlier and

improve treatments, but helping people understand how they can reduce their

risk of developing cancer in the first place remains crucial in tackling

cancer."