Cancer in most cases may be the result of biological bad luck rather than caused by genes or behavior, with the random division of stem cells making people more vulnerable to mutations, a new study shows.
A formula that plotted the number of stem-cell divisions over a lifetime against the risk of cancer showed a correlation and explained two-thirds of cases, according to a research paper published this week in the journal Science. The study, conducted by mathematician Cristian Tomasetti and geneticist Bert Vogelstein of Johns Hopkins University, is based on previously published cancer statistics.
The research may bolster arguments that cancer often can’t be prevented, with risky behavior such as smoking and excessive exposure to the sun being less of a cause than chance. That would support focusing more resources on diagnosing the disease in early stages and on treatments to reduce mortality rates.
The researchers cautioned that the study isn’t a license to engage in unhealthy behavior. “Cancer-free longevity in people exposed to cancer-causing agents, such as tobacco, is often attributed to their ’good genes,’ but the truth is that most of them simply had good luck,” Vogelstein said in a statement.
Tissue types that have more stem-cell divisions are more prone to mutations that can lead to cancers, with data demonstrating a statistical correlation between the two, Vogelstein and Tomasetti said in their paper. They suggest that only one-third of the variation in cancer risk may be due to environmental factors or inherited predispositions.
The researchers focused on stem cells because they live longer, with divisions of the self-renewing cells maintaining the tissue’s stability while also having the capacity to initiate a tumor. Random mutations -- or bad luck -- occurring during the replication of noncancerous stem cells, which typically account for a small number of the total cells in tissue, can lead to the disease.
The lifetime risk of being diagnosed with lung cancer is 6.9 percent, while that of thyroid is 1.08 percent and brain cancer is 0.6 percent, according to published statistics. Acknowledged risk factors that explain some of the incidence include smoking, alcohol consumption, ultra-violet light and human papilloma virus, as well as genetic variations.
To explain the remaining cancer risk, the researchers from Baltimore, Mayland-based Johns Hopkins focused on 31 tissue types. The positive correlation between the number of stem-cell divisions and lifetime risk of the disease was seen among different types of cancers with varying levels of incidence.
Some cancers, including breast and prostate, weren’t included in the report because reliable stem-cell division rates haven’t been determined, according to the study.