Stop the blame game, genetic study shows most cancer is caused by random mutations

Guilt, blame and shame.

 

Three words that shouldn’t be attached to a cancer diagnosis, yet I have been repeatedly told by patients that they feel these three powerful emotions – guilt, blame and shame.

 

“Did I get cancer because I smoked for two years at uni?” 

 

“Why me? I exercise, I am a vegan and I don’t smoke.” 

 

Well, the fact is that “cancer” is an umbrella term for many different types of cancer. For each type of cancer, and even within each type of cancer, there are multiple causes, many of which are not fully understood.

  [If you want a refresh over the basic idea of what cancer is before reading this post then check out http://www.fittermummy.com/what-is-cancer/]

We know that mutations, mistakes in the cells DNA, cause cancers but what causes these mutations to happen in the first place?

  1. DNA copying errors

The first factor is the random errors that occur every time a cell divides to make two new cells. The cell has to copy its DNA to make two new cells. This routine process happens millons of times a day in everyone’s body.

 

You have 100 million million cells in your body. That is 100, 000,000,000,000. To put that into context there are more cells in your little finger alone than people in China. It is estimated that there is a cell turnover of 50-70 billion A DAY in an adult.  Each time the cell makes a new cell, it copies a new set of DNA for the new cell. It is at this step that potential mistakes are made. These errors happen all the time and are not of consequence unless they affect an important gene rather than an unimportant gene. It is a matter of probability. To be honest, when I look at the numbers, I think what a wonder it is that more mistakes are not made.

 

  1. Environmental factors

 

The second factor is environmental or lifestyle-causing mutations. Some people add to the number of mutations by their behaviour, for example if they suffer excess UV exposure from sunlight, or if they smoke.

 

  1. Inherited mutations

 

The last fact is inherited, genetic mutations passed on from your parents.

 

Earlier this year Vogelstein, Tomasetti and Li published a paper in Science entitled:  Stem cell divisions, somatic mutations, cancer etiology, and cancer prevention

 

Vogelstein, Tomasetti and Li studied  17 cancer types in 69 countries around the world.  They looked down at the DNA mutations thought to have caused tissue to become a cancer.

 

The authors of this paper found that averaged across all cancers 66% of the causative mutations are simply a result of DNA copying errors.

 

When the authors looked for inherited DNA faults, it only made up 5% of the causes. This would be things like BRCA.
Lastly they found that 29% are attributable to lifestyle or environment.
An important twist in the story is that some cancers were found to contain a much higher percentage of lifestyle-related mutations. The most obvious being lung cancer. In lung cancer they found that 65% of the DNA mutations could be linked to lifestyle (the obvious one being smoking). Only 35% were copying errors.

 

This still means that 35% (a huge number) is NOT related to lifestyle!
On the opposite side of the “type of cancer” spectrum sit prostate, brain and bone cancer with a 95% incidence of random copying errors, linking them more closely with cell turnover errors and less with lifestyle factors.

 

So statistics show that it is not usually lifestyle to blame when someone develops cancer. 

But we can all feel encouraged to get to work on lowering our own personal risk by adopting a healthy lifestyle in certain cancers there is a large benefit for healthy living. We must remember that a healthy lifestyle may help fight cancer in ways beyond altering the DNA. This is by altering hormonal profiles, metabolism, gut microbiome, your immune system detecting and destroying these mutated cells etc. These benefits of a healthy lifestyle should not be discounted but I still think we need to get rid of the guilt! The majority of cancer sufferers did not “bring it on themselves”.  Lastly this paper also reminds us that no one is immune, no matter how healthy your lifestyle if you have symptoms get them checked! 

 

In summary:

  • Many people will develop cancer, no matter how healthy their lifestyle.  
  • A cancer diagnosis is a pivotal point in your life at which you can review your life style choice and resolve to make positive lifestyle changes.
  • But the re-assessment of the lifestyle should not be at the sake of your overall mental health and wellness.
  • No matter how healthy your lifestyle please don’t be complacent about your health, if you have symptoms get them checked. Nobody is immune. 
  • If you take nothing else from this post I want you to stop the guilt, the shame and the blame game.

 

You can access the article here:

Stem cell divisions, somatic mutations, cancer etiology, and cancer prevention

 

 

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  • Fascinating to read Ailsa. I am most taken with the statistic that 65% of mutations are linked to lifestyle in lung cancer- from my experience I would have thought the figure was much higher than that. Is that statistic specific to lung adenocarcinomas or does it include other types of tumour?

    • The study was conducted using mathematical modelling and known genetic function. Whole genome sequencing and gene function has come a long way but it is not like we fully understand it yet. I also believe the gene mutations are not the full story of cancer, the immune system and epigenetics play a role too. They used the large cancer databases from each nation and I imagine there is some dilution of the data by having to merge groups as this data would have been collected not for this purpose. As we now know breast cancer has multiple genetic subtypes as does lung realistically. Their hypothesis is coming from the stem cell cell division potential of each tissue. Ultimately you need multiple mutations in a cell in key genes to make a cancer. With lung cancer they found a really wide spread of varying mutations indicative of the fact that they were caused by mutagens. Rather than a repetitive copying mistake. The paper has caused quite a lot of controversy as the authors present it from a point of view that early detection is more important than preventative measures. Personally I think the data actually aligns well with the epidemiologists predictions and actually reinforces the need for a combination of screening, prevention and health awareness. Sorry waffling response. Google vogelstein and science and you get a lot of discussion around it.