Where's the absolute, irrefutable proof that cigarettes cause cancer?

In humans of course. ( If you smear enough tar on a rat long enough, he will probably develop cancer.)

If someone has the answer, I guess this might well belong in General Questions. If that’s the case, then so be it.

And I haven’t posted this to debate whether or not cigarettes do cause cancer( however please feel free). I am asking for proof of a direct medical link from cigarettes to cancer. Sure a lot of people have died from lung cancer that smoked but alot of people haven’t. My dad smoked all of his life and died in his sleep at 78.

So my question is this. Is there an absolute, irrefutable medical link that smoking causes lung cancer? Anyone?

Oh and I haven’t smoked in 25 years.

No one knows exactly what causes cancer, we only know what can increase the risk of causing cancer. In the case of smoking studies examine the rates a of lung cancer in smokers versus non smokers. It is clear from these studies that smoking increases a person’s risk of lung cancer.

It is mistaken to think that everyone will get cancer after they smoke a certain number of cigarettes. Its all about risk and percentages. It doesn’t necessarily apply to everyone. You can’t ask a cancer researcher if someone who has smoked 2 packs a day for 50 years will have cancer or not, just what their increased risk would be.

Its hard to give a cite for this because near every study that’s ever been done has shown an increased risk of cancer associated with cirgarette smoking in humans.

As far as absolute, irrefutable proof there isn’t any. And there isn’t any proof of anything in science. There is merely evidence that supports or rejects a hypothesis. There hasn’t been any evidence that rejects the hypothesis that smoking increases the risk of lung cancer, that I have seen. That said, there also isn’t any evidence that proves the link beyond any doubt. Science doesn’t work that way.

because you have a sample pool of one person that smoked and did not get cancer, does not prove that smoking doesn’t in some way have a link to cancer. Causing it? let’s see.

All smokers do not get cancer.
People who do not smoke get cancer.
Does that mean that there isn’t a link between the two? No.

Perhaps part of the problem is how you have the question phrased. there are diseases that have causal factors. The flu, measles etc. If you get the virus, you get the disease, it may be in lesser or greater intensity, but you get the disease.

Cancer is a term for a large quantity of diseases that each have different properties etc. each of them occur for different reasons, and science has NOT established the exact chain of events in each one of them. If they had, it’d be a simple process - don’t want colan cancer, don’t eat parsnips or whatever the cause was determined to be. However, with cancers, in general, we don’t talk about causing in the same respect as the rhinovirus causes the flu. We talk, instead about increasing your risk. In addition, we cannot, at this point determine how any single individual got the cancer they did, we can sometimes eliminate other potential risk factors and are left with one as being the likely culprit. If you are taking the case of Lung cancer, there are many things that are linked to a higher probability - smoking is one of the highest, but not the only one.

For another example - drinking and driving certainly increase your risk of : Being incarcerated, getting into an accident, getting your license revoked.

Does this mean that all people who drink and drive get incarcerated etc? no. Does this mean that if you drink and drive next Saturday night at 6 pm you will get incarcerated etc/ no. Does this mean that If you drink and drive you are increasing your risk of incarceration etc? you bet. Does this mean that if you drink and drive and you DO get into an accident, get your license revoked and get incarcerated, was the drinking and driving the CAUSE of it? Probably (but not necessarily always).

So, when we say Drinking and driving cause accidents, incarceration, loosing licenses, are we wrong to use that phrase? No, because we can show a causal link in individual instances.

But because we cannot say a specific individual’s cancer was directly caused by that individual’s specific behavior, are we wrong to say that the most likely causal factor was the specific risk factor? Nope, IMHO, barring scientific breakthroughs in cancer research.

Science does not work that way. Hypothesis are tested and false hypotheses can be demonstrated incorrect (within the framework of experimental error, faulty assumptions, etc.) Science has no way of offering absolute, irrefutable proof of anything.

If I lined 100 men up and fired a .45 round into the temple of each, and they all died, it would still not prove that if I fired a .45 round into your temple you would die.

Nevertheless, would you volunteer to be person 101?

What is your definition of a .45 round? What is your definition of “temple”? What is your definition of death?

Come on, there comes a point where arguments like that become utterly ridiculous.

Please allow me to quote an article I wrote about Cancer: The Evolutionary Legacy, by Mel Greaves:

*Smoking causes cancer.

By now, just about everybody accepts this statement. But what does it mean? Not everybody who smokes gets cancer. Not everybody who does get cancer gets the same type, though lung cancer is certainly the most common. But not everybody who gets lung cancer smokes.

So what, really, does it mean to say that something causes cancer? For that matter, what is cancer and how has it managed to survive throughout human and animal evolution?

Cancer is a complex disease driven by a multitude of factors. Whether or not a person is stricken by cancer may have to do with all of the above, none of the above, or even simple chance.

“We’ve been naive about the singularity of causes,” says Greaves.

There are definitely cases where a likely cause for cancerous mutations to cellular DNA can be pinned down, such as with smoking. Most cases, however, involve a multitude of factors such as genetics, the environment, diet and exercise, and even random chance.*

There’s a lot more to the article, and if you want to check it out, e-mail me for a link or search for it at Themestream, where it’s posted. But the point is that you can’t necessarily point to something and say, “You got cancer because of X.” Smoking is an exception in some ways because there have been so many studies done on it. But even so, if you smoked and you get lung cancer, did the smoking necessarily contribute to it/cause it? No. You might still have gotten it without the smoking (maybe you were a coal miner, too). But if large-scale studies are done showing that a lot more people in the “smoking” group get cancer than those in the “non-smoking” group, all other factors being considered, then it looks pretty likely that smoking contributes to (causes) cancer. And that is exactly the situation we have. This doesn’t mean that everybody who smokes will get cancer, just that they have a greater chance. Kind of like the lottery. If I buy 1 ticket and you buy 100,000, you have a greater chance of winning. But that doesn’t mean you necessarily will or that I necessarily won’t.


I often conclude that we have reached that point when people start asking for absolute, irrefutable proof in a discussion of science.

I could simply have stated it as baldly as you did, but I prefered to trust the ability of my audience to interret the message.

Spiritus Mundi sed:

I assume that means that my OP question was ridiculous however I have always traveled under the assumption that no question asked in earnest is ridiculous since the asker would learn something from it.

However the term “cigarette’s cause lung cancer” has been bandied about so much in the last 30 years that I thought the question begged for the asking. And at the risk of showing my ignorance, I will admit that I have in fact learned something from the responses.

At any rate, for most all diseases, especially rare diseaeses such as lung cancer, one basically has to show a doubling of the occurance of this disease in an experimental group, or failing that, an observational category, often reported as a coefficient such as 1.15 showing a relatively negligable increase in the prevalence of this disease by 15% and most likely a lack of an epidemiological link between action or condition A and disease B. At any rate, if you wanted to find “absolute, irrefutable proof” then this is commonly considered the benchmark for proof, but then again, nothing is absolute. I am not going to spend time on finding an actual cite to individual studies or even meta-studies. If anyone was truly interested, I am sure that you could easily locate on the WWW these studies with fair representation to all studies, regardless of the end result of the study.

OK, aha, time for the test. What did you learn? :wink:

David B I know there is something to be learned here. Just give me more time to study ok?

threemae sed:

I thought I had my answer here but then threemae went on to say:


Given confidence intervals, relative risk factors, dose-response curves, etc. etc., I belive the question over whether smoking causes lung cancer is basically sealed. No person with common sense could argue against this hypothesis, given the amount of data which supports it.

But, disregarding Ockham’s Razor (and given the fact that I lack common sense), you can say that the causative effect of smoking in lung cancer can be disregarded. For instance, the desire to smoke can be correlated to a risk of lung cancer. Let’s say the desire to smoke is linked to a polygenic Non-Mendelian trait which is correlated to a specific of brain chemistry. This trait is gradated - some people have more desire to smoke (and thus smoke more), some people have less. Smoking just serves to balance the brain chemistry and is a self-adaptive response. Now, one of the aspects of the phenotype of this genetic milleu (that causes the altered brain chemistry) is that you have a preponderance to lung cancer. This is firmly tied to the gradation of the trait, such that a 40 pack-year smoker has a 5 times greater relative risk for lung cancer than a 10 pack-year smoker.

Some people who smoke and don’t get lung cancer are people who have become addicted to nicotine but lack this genetic milleu.

People who get lung cancer but don’t smoke are either people with modifiers that lack the desire to smoke, or have never discovered the self-adaptive response of smoking.

Similar situations to the above situation have been seen – certain pharmacogenetic traits cause specific personality traits and inability to metabolize certain drugs.

Anyway, it just is illustrative that good data is totally independent of whatever hypothesis it is meaning to test. Another reason proof is elusive in science.

Not in the least, Aha, and I apologize if I gave that impression. I understand the need to be utterly clear on things.

I think everyone knows that smoking doesn’t guarantee a cure for cancer. So let’s get past that and move on to simpler things.

Is smoking good for you? I’ve never heard of any reasonable evidence that suggests so. Is smoking bad for you? Well, while it may not cause lung cancer, it certainly appears as if there’s some relation between smoking and development of cancers, major or minor though it may be. In addition, I’m curious as to what the lung capacity of the average lifetime smoker would be… and then there’re things like yellow teeth, tar-lined throat, etc…

In short… there’s really no point in smoking, is there? :smiley:

Oh, and I just remembered…

In the OP, Aha said…

Well, smear a person’s lungs with tar long enough, and he will probably develop cancer too, right?

There is no irrefutable proof that smoking causes cancr, a “fact” which the tobacco companies are fond of reiterating.

There is, however, a strong correlation between smoking and lung cancer. Repeated studies have shown that smokers are about ten times more likely to get lung cancer than non-smokers. The first major study to prove the link was published in Britain in 1950 by Doll and Hill (Cigarette smoking and lung cancer (Doll and Hill British Medical Journal 1950 ii 739-748). I can’t find a copy of the paper online, but given the cite, somebody else might be able to.

Lung cancer is very rare in the non-smkoing population, so even if you multiply the risk by ten, smokers are still relatively unlikely to die of lung cancer. They are much more likely to die of coronary artery disease: although the relative risk of coronary artery disease associated with smoking is only about 1.7 (i.e. a smoker is 1.7 times more likely to get it than a non-smoker), it is much more common in the general population. It’s a small but significant increase to a big risk, rather than a big increase to a small risk.

Broadly speaking, if you take a large group of smokers of various ages and compare them to an age-matched group of non-smokers (i.e. you have to have the same number of 30 year-olds, 76 year-olds, etc. in each group), the relative death rate of the smokers is about 1.6. Put crudely, a smoker is 50% more likely to die at any given age than a non-smoker (though obviously they’ll both die eventually).

Now, it could be that the gene which predisposes some people to smoke also predisposes them to get cancer and heart disease, though there’s no evidence for this. It could be that “smoking-related” diseases are in fact related to poverty (poor housing, diet, etc.) and that a greater proportion of poor people than rich people smoke. There is some evidence for that, but the risks associated with smoking were first established in the 1950s when smoking was much less a function of social class. It could be that the risks associated with smoking are not to do with smoking per se, but come from the chemicals in matches or lighter fuel (no evidence for this either).

It could even be, as others have suggested, blind chance. All those studies into smoking and lung cancer, involving hundreds of thousands of people (if not millions) could still have inadvertantly selected groups of smokers who were more prone to lung cancer anyway. Likewise, it could be pure coincidence that, up till now, things have always moved downwards, rather than upwards, when dropped. Or that the Sun has always risen in the morning and set at night.

In other words, it depends what you mean by “proof”. On the skeptical/Popperian view of science, nothing is ever proven. For classical skeptics (e.g. David Hume), there is simply no proof there to be had; what scientists term “causation” is merely “constant conjunction”. For Popper, there is only failure to disprove, though it’s difficult to see how you could disprove the hypothesis that smoking leads to an incerased risk of lung cancer: Popper’s model works quite well with yes/no type questions and less well with relative risk. (Popper’s model also, incidentally, comes so far short of describing how scientists actually work as to be laughable.)

If by “proof” you mean the generally-accepted standards of medical proof: that is, the kind of steps you would have to go through to prove that a drug was safe and effective before it could be licenced, then the proof is pretty irrefutable: if you compare large numbers of smokers with large numbers of non-smokers, then the smokers are ten times more likely to get lung cancer. It’s as simple as that.

No apology necessary spoofers. :slight_smile:

And yep you are right. If we smeared enough tar on our lungs we are bound to develop something.

TomH, thanks I really learned something from your post as well.