Is Cancer Mostly About Bad Luck?

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One of Susan Sontag’s biggest revelations from her celebrated book, Illness as Metaphor, is that getting sick means more than taking on just a disease. A lot of undeserved baggage comes with it—including judgments about how your lifestyle caused the cancer to happen.

Historically, some diseases have carried positive associations. Before we understood  tuberculosis, for example, it was considered an illness of artists, and reflected well on the character of the victim. HIV, on the other hand, was viewed as a reflection of an excessive lifestyle and weak character—a view that may have hindered our efforts to develop treatments. Cancer bears a similar stigma: You got cancer because you smoked, or you drank alcohol, or you didn’t exercise enough. But a new study has turned that notion on its head.

A Matter of (Bad) Luck

Why do we really get cancer? A study in the journal Science offers a startling answer: Most of the time, it’s just bad luck. The cells in our body are dividing all the time, in particular, the stem cells—the cells that constantly replicate to maintain the health of our body’s tissues and organs. Every time they divide, mistakes are made in the DNA molecules that govern the cell’s behavior. Our cells have multiple mechanisms to repair these mistakes, but sometimes the repair mechanisms fail and the cells begin to grow uncontrollably. That’s when they become cancers.

Using a statistical model, the authors of this study were able to show that approximately two-thirds of all cancers are a result of these random mistakes. The equation is simple: The more a particular stem cell type divides, the more mistakes and the greater the likelihood of cancer—independent of other factors. That’s why colon cancer is more common than cancer of the small intestine, or why basal cell skin cancer is more common than melanoma.

This correlation between stem cell divisions and cancer incidence is striking, alone accounting for two-thirds of all cancers. Hereditary factors appear to determine only about 10 to 15 percent of cancers, and environmental factors such as smoking, alcohol, diet, and lifestyle account for the rest. In some cancers, the role of lifestyle factors is profound—smoking and lung cancer, for example—but even so, the impact of smoking is stacked on the already-high rate of random mutation in pulmonary (lung) stem cells.

Your Lifestyle Matters

That doesn’t mean you should stop making healthy lifestyle decisions—they still matter a great deal. However, in many cases, it is not what we do, but rather luck of the draw that’s responsible for our health—at least as far as cancer is concerned.

This may be comforting for some—you can stop blaming yourself if you get cancer—and disturbing for others—the loss of control may be frightening. The key to containing cancer, at least for the two-thirds that are caused primarily by random mutations, is early detection and better treatments.

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The One Medical blog is published by One Medical, an innovative primary care practice with offices in Boston, Chicago, Los Angeles, New York, Phoenix, the San Francisco Bay Area, Seattle, and Washington, DC.