Given this widely accepted view, it was surprising last year when one of the world’s leading cancer scientists, John Hopkins University researcher Bert Vogelstein, together with mathematician Cristian Tomasetti, claimed that cancer is much less preventable than we thought. In a widely reported study, they argued that unavoidable, random DNA mutations, which occur routinely in our cells even in the absence of carcinogens, are “the major contributors to cancer overall, often more important than either hereditary or external environmental factors.” Cancer is often due to, in their words, “bad luck.”
As evidence for their claim, Tomasetti and Vogelstein presented a striking correlation between the lifetime risk of certain cancers, and the number of times cells replicate in the body tissues where those cancers arise. Why is the number of cell replications important? Because each time a cell replicates, a new copy of our DNA is made, and random mutations inevitably occur in the process. These mutations can’t be prevented, no matter how carefully we avoid carcinogens — the biochemical machinery that copies our DNA is very good, but not perfect. So each time a cell replicates, there is a fresh opportunity to be unlucky, by picking up a harmful mutation. Tissues with more replicating cells, like skin and colon, are therefore much more likely to acquire a cancer-causing mutation than tissues with fewer replicating cells, like brain and bone. “No other environmental or inherited factors are known to be correlated in this way across tumor types,” Tomasetti and Vogelstein noted. The implication is that prevention won’t be effective for many cancers. Mutations happen, and we can’t do much about it. Instead, we should focus on better screening to detect cancers early, when they can be treated more successfully.