CBC’s The Sunday Edition had a parade of cancers researchers on the show through November and early December in an attempt to satisfy a continuous stream of outraged listeners. It started out as a conversation about why cancer screening recommendations have been reduced prompting irate listeners to wrote in saying their daughter was getting every sort of cancer screening regardless of what the guidelines say. Of course, they forget that screening has important risks associated with it as well. But that’s another story.

To quell that storm, the following week another guest came in to talk more in depth about cancer screening but this guest then made the mistake of mentioning how many cancers can be attributed to behaviours such as obesity and smoking. In fact, the guest said, behaviours cause more cancers than environmental toxins despite host Michael Enright prodding her to say otherwise. Cue another deluge of angry letters saying that ‘isn’t it obvious that the toxins in our environment are causing pretty much all our cancer and shame on this researcher for blaming the victims of cancer instead of the big corporations spewing all these toxins!’ Whoa. That was intense.

When it comes to blaming the victim, these people have it entirely backward. Epidemiology cannot, ever, point to a person and say with certainty that their cancer was caused by x, y or z. Even if a three-pack-a-day smoker got lung cancer, there’s always the chance that something else caused the lung cancer.

What epidemiology can do is to look at two groups or people who are as similar as possible in every way except one being obese and the other not (which, especially in the case of obesity, is very difficult to do). If it turns out one group has more cancers than the other, epidemiologists can attribute it to obesity. Epidemiology can only ever tell what might affect your risk of cancer, it can never say why a particular person actually got cancer.

The only way we could ever blame a specific person for their cancer is if we went back in time, made them not obese in this case, and ran the clock forward again to see if they still got cancer. If they didn’t, then you could say their obesity, in some way, caused their cancer. We’re a long way from time travel so we’ll have to settle for the first approach I described.

What’s more is it’s clear that the public, and more than likely a good chunk of those angry listeners, do blame victims of cancers in some cases. I can’t find the data right now but which cancer charity do you hear the least about: breast, prostate or lung? Why do you think that is?