Cancers due to bad luck, left, and cancers due to a combination of bad luck, environmental factors, and inherited factors. Elizabeth Cook]

Cancers due to bad luck, left, and cancers due to a combination of bad luck, environmental factors, and inherited factors. / Elizabeth Cook]

Nearly two-thirds of all cancers are caused by random mutations of the body's stem cells, not by hereditary or environmental effects, according to a study released Jan. 1 by Johns Hopkins scientists.

Tissues with the most divisions of regenerative cells and hence the most chances for mutations tend to have the greatest rates of cancer, the study found.

This explains why skin cancers, for example, are far more common than bone cancers. Skin cells die constantly, so they must be replenished far more often than those that make bone, introducing more chances for errors that lead to cancer.

In effect, most cancers come down to "bad luck", the researchers say in the study.

The findings introduce new dimensions to the struggle against cancer, said two researchers who did not take part in the study.

The study was published Thursday in the journal Science. Cristian Tomasetti of the Johns Hopkins Kimmel Cancer Center at Johns Hopkins Medicine in Baltimore is first author. The study's senior author is Bert Vogelstein, also of the center, part of Johns Hopkins University.

Healthy diet and protection against carcinogens are still important, said Tomasetti, because the one-third variability is still substantial. And the proportion of randomness in each type of cancer varies. Some cancers tend to be greatly increased by environmental factors, such as lung cancer in smokers. The two-third average is a summary of the risk of cancer from all tissue types.

Strong relationship

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Most cancer is bad luck, study finds