Friday, 18 December 2009

Another scare story

Apparently smoking 15 cigarettes is enough to mutate your genes.

If that's true, I'm now a whole new species.

If it's true, then let the coppers have your DNA then take up smoking. By the time they come back to get you, your DNA has changed into someone else's.

If there is any truth at all in that story, the DNA database is a total waste of time because smoker's DNA is changing too fast to monitor.

There is no truth in it, naturally. The sequencing of the cancer they mention took place on one cancer from one patient. Not mine and not yours. Mutations do not happen in any sort of logical sequence and a mutation can even be accidentally fixed by a subsequent mutation. If you're having one every 15 smokes you're mutating faster than bacteria.

Not all mutations cause cancer. Most of your DNA is junk so mutations in that part do nothing. Not all mutations are detrimental (although most are) and mutations do not occur in all parts of your body simultaneously. They occur in one cell. You have a lot of cells. No cell lives forever, all are replaced and broken ones are replaced earlier. The chance of cancer from any activity is not as great as advertised. The risk rises with age because of the laws of chance - the longer you're around and getting mutated (by UV light, by food components, by breathing traffic fumes, by having hot showers which vapourise the chemicals added to water - a million risks, even for non smokers) the greater the chance of one of those mutations producing a nasty.

Chance, of course, isn't so simple. 'One in a million' does not mean you can do something 999,999 times and then stop. The 'one' can be anywhere in the 'million'. It can be first just as well as it can be last. So babies can potentially get cancer the moment they pop into the light.

Exposure to the same carcinogens every day gives you the same risk today as yesterday and tomorrow. It's like playing the same numbers on the lottery. One day the numbers might match but the chance of a match is the same in every draw. The chance doesn't increase. The number of attempts increases.

So it is with cancer. The chance of getting cancer (from any routinely-experienced source) today is the same as yesterday and the same as tomorrow. As you get older, you've just played more hands and so the accumulated plays mean you could get the match just by persistence. You might never get it. There was once a story in the local paper here about a 90-year-old woman whose budgie died of 'passive smoking'. We smokers took it to heart, knowing a little history. When the canary dies it's time to open a window. The budgie in question was nine years old, which is Zimmer frame and Stanner perch-lift time for such birds. The old lady was fine.

There are genetic predispositions to cancer, as there are genetic predispositions to all sorts of things. If cancer runs in the family you should watch your step with exposure to known risks, just as if colour blindness runs in the family you should avoid getting sold a Barbie pink car by a salesman who insists it's pale green. If there's no cancer in the family, that doesn't guarantee you won't get it. It's a lottery.

One cancer in one person cannot be extrapolated to the whole population. Biology scoffs at such notions. Even if you studied every person in the world but one, that last one could be very different from your conclusions. Biology pays scant attention to statistics. Especially the motor-mechanic variety so beloved of the ban brigades.

Unfortunately, government doesn't.


Anonymous said...

Parts of that were clear as crystal, while others were clear as mud.

Your certainty as to how cancer arises is not matched (at least in my reading) by the evidence. In fact, we have lots of very good theories about how cancer arises, but a lack of very good answers.

For example, how do viruses, versus asbestos fibres, versus the theory that cancers are 200-odd different diseases, etc. co-exist with your "it's all random chance" theory.

I'm playing a bit of devil's advocate here, but I really get a bit annoyed when someone starts rabbiting on with certainty about what causes cancer. We have loads of theories, but no feckin idea, at the end of the day.

Frank Davis said...

The Telegraph has an article about cancer by Karol Sikora.

No mention in it at all about smoking, which absolutely everybody knows is what causes cancer. And heart disease. And in fact all diseases.

Funny that.

I hope somebody has a word with Karol Sikora to put him right on this point, so that he doesn't waste time and money futilely searching for something that's been perfectly well understood by top boffins for donkey's years.

Anonymous said...

They took a sick cell and a healthy cell from the same patient and compared them.

scientific method has really changed since the days I learned the rules of ecperimental design. Two cells from the same patient, um well, what can one say to this, the patient is sick, but some of his cells are considered a healthy control? Jeez, I don't know where to start with the criticism of this. I think I will just go and sit in a corner and mourn the passing of the concept of "control" in science along with outdated ideas like, ethics and get the results BEFORE you publish the paper.

Leg-iron said...

Anon #1 - I don't express any certainty on how cancer arises and didn't define causes to the exclusion of all else.

The point was the chance of it happening in any one individual at any particular time. Even with exposure to a known carcinogen it's still random.

Take the virus example. You firstly have a random chance of encountering someone with the virus. If you do, then you have a random chance of being infected and if you are infected, you have a random chance of it producing a cancer at any particular time.

None of the steps are definite, and no step definitely leads to the next.

Then there's the chance that your immune system will catch the cancerous cell before it gets out of control. That happens a lot.

There are many possible causes of cancer, but even regular exposure to a known cause does not guarantee you'll get it.

Leg-iron said...

Frank - they'll get to it.

Leg-iron said...

Anon #2 - if that's the case, then the 'healthy' cell would have been subject to the same rate of mutation over that smoker's life as the cancerous cell. It will be just as damaged. It just didn't get the mutation that turned it cancerous.

In effect, they've doubles the estimated rate of mutation because no two cells will get exactly the same DNA damage from a particular source.

They've also attributed all those mutations to smoking, and none to anything else.

Sometimes mutations come about because of errors in DNA copying during cell replication, with no outside influence at all.

Sometimes, they just happen.

You're right. It's propaganda, not science. There's a lot of it about.

Anonymous said...


Thanks for that. Unfortunately, until we either understand exactly how cancer arises (eg. is it a mutagenic process, is it aneuploidy, is it really 100 different diseases?), rather than just theorising about it, or until we can reliably cure it there will be no effective way to counter the anti-smokers' nonsense.


Anon #1

opinions powered by