In recent weeks, there has been a lot of talk in the news concerning the role of ‘bad luck’ in the development of cancer, and that same talk is set to expand to connect with the topic of breast cancer associated with pregnancy. There are a couple of reasons why you should not be distracted or worried by any of this. First, years of research suggests that pregnancy may be some slight positive and slight negative effects on risks of certain cancers, plus there is on-going research looking at connections between pregnancy and certain breast cancers triggered by hormone changes. But there is no smoking gun, so any real influence of pregnancy at most would be one factor in an ocean of influences.
Second, it’s important to know that the recent discussions about the ‘bad luck factor’ have been very much distorted in popular media, so let’s unpack that a little. Recently, there have been articles on reputable news media, such as CNN and NPR with headlines like “Bad luck mutations increase risk more than behavior, study says” and “Cancer is Partly Caused by Bad Luck, study finds”.
Few people would disagree that bad luck is a factor, but many stories have used specific numbers, especially 67 percent, implying that “bad luck”, and not life-style or environmental factors, account for two out of three cancer cases. Furthermore, some publications that I will not even name have gone as far as to say that the ‘study’ results mean that you may as well smoke, or do other things that have been found to be associated with cancer, since it all comes down to luck. But that would be completely wrong.
How did this all start? About two years ago, there was indeed a study that looked at numerous types of cancer all at once, and found that 67 percent could be attributed to genetic errors occurring in the division of stem cells to create more body cells. It was published in Science, a very good journal, but the authors emphasized that they were not looking specific, common cancers, but they also wrote:
“These results suggest that only a third of the variation in cancer risk among tissues is attributable to environmental factors or inherited predispositions. The majority is due to “bad luck,” that is, random mutations arising during DNA replication in normal, noncancerous stem cells.”
There was a lot of criticism from other scientists, but the popular media picked up basically one line, that one third of cancer depends on controllable factors, and therefore that two thirds were due to ‘bad luck’.
Not only is this misleading, because the story changes if you look at different types of cancer separately. With lung cancer, for instance, only 35 percent or so involve random factors. The rest come from controllable environmental factors, mostly smoking. Thus, interpreting the study results to mean that avoiding smoking won’t be that helpful is 100 percent wrong. And that’s a percentage about which you can be very sure.