I am just trying to say that things that cause cancer are not as deterministic as we think.
to develop a cure, we must better understand the causal mechanisms.
this starts with acknowledging what we know and don't know about a devilishly complex disease that is arguably better conceptualized as a broad category rather than one monolith -- similar to how the flu, cold, and covid could be grouped under one mega classification, but are better identified as distinct conditions.
The reason why only 20% of smokers get cancer is similar to why a person doesn't get cancer after 1 cigarette.
This is only counterintuitive if your default thinking is that smoking=cancer. In reality, there are a lot of variable chemical and biological processes involved, but ultimately it ultimately boils down to a cumulative risk, not guarantee.
Longer answer: Logically, the answer should be zero, but it's actually not that simple to categorise either 'non-smokers' or 'a smoking-related illness'.
Taking lung cancer as an example, approximately 10-20% of lung cancers occur in folks who are non-smokers (defined as 'never' or 'fewer than 100 cigarettes in their lifetime'). Researchers estimate that of these, around 20% are caused by second hand smoking, meaning that around 8-16% of lung cancers are non 'smoking related' in non-smokers. Not all lung cancers result in death.
So if we take the same approach, and consider the 80% of lung cancers which occur in smokers, presumably similarly 10-20% of those would have developed lung cancer regardless of whether they smoked or not, so potentially we would need to say that less than 65% of lung cancers are caused by smoking.
Is it then fair to call lung cancer a 'smoking-related illness', if more than a third of people who develop lung cancer did not do so because they themselves smoked[0] (the number changes to 70% if we consder the folks who hypothetically develop lung cancer due to second-hand smoking as 'smoking-related').
There are also a lot a problems with the methodology here. How do we know whether someone really smoked 100 cigarettes or fewer? Is there any statistically significant difference between people who smoked 100 and 1 000? 100 000? Does it matter if someone smoked all of those 10 000 in the last year (almost 30 a day) or whether they smoked those 10 000 over the past 50 years (less than a pack a month)? All of these things seem to my mind to be problematic and make it impossible to answer your question.
I suppose that means that I was overconfident in my assertion in the parent comment that '7/10 smokers die of smoking-related illnesses'. It was not unresearched (although uncited) and I got this number from this article: https://www.washingtonpost.com/news/wonk/wp/2015/02/26/the-t..., which in turn reported on this study: https://bmcmedicine.biomedcentral.com/articles/10.1186/s1291....
However, perhaps I wasn't critical enough in my reading, and instead simply parroted the stat.
[0]: big caveat here is that my ramblings don't consider the possibility that a 50 year-old who would otherwise have developed lung cancer at 80 develops lung cancer as a result of smoking, and lung cancers caused by smoking stop lung cancers developing from other causes.
