Infections causes 16% of cancers–what?

Ed Yong, a scientist and contributor to Discover Magazine, wrote an blog post, What does it mean to say that something causes 16% of cancers?, discussing a news report that stated that 16% of cancers around the world were caused by infections.  Here are some excerpts:

A few days ago, news reports claimed that 16 per cent of cancers around the world were caused by infections. This isn’t an especially new or controversial statement, as there’s clear evidence that some viruses, bacteria and parasites can cause cancer (think HPV, which we now have a vaccine against). It’s not inaccurate either. The paper that triggered the reports did indeed conclude that “of the 12.7 million new cancer cases that occurred in 2008, the population attributable fraction (PAF) for infectious agents was 16·1%”.

But for me, the reports aggravated an old itch. I used to work at a cancer charity. We used to get frequent requests we got for such numbers (e.g. how many cancers are caused by tobacco?). However, whenever such reports actually came out, we got a lot confused questions and comments. The problem is that many (most?) people have no idea what it actually means to say that X% of cancers are caused by something, where those numbers come from, or how they should be used. Continue reading “Infections causes 16% of cancers–what?”