Cancer Mystery

So far the story sounds simple: Radiation damages DNA. Repairs are bungled. Cancer ensues.

But it's not so simple, says Dicello, not at all. Radiation can affect human tissue in unpredictable ways, and the chain of events leading from radiation to cancer is vexingly complex. "If I really understood it, I'd probably win the Nobel Prize."

Consider the following: Some astronauts, veterans of long space missions, have "significant chromosome aberrations" in their blood cells. These aberrations may be "associated with the development of cancer," says Dicello, but they do not, by themselves, cause cancer. For that to happen, cells with aberrations must undergo a series of further mutations. According to the National Cancer Institute, "the number of cell divisions that occur during this process can be astronomically large--human tumours often become apparent only after they have grown to a size of 10 to 100 billion cells." Years, even decades, might pass between the onset of the problem, the exposure to radiation, and the appearance of a tumour.

Because of the delay, it's very difficult to determine exactly when or why a cancer starts. That's the bad news.

The good news - for astronauts and for the rest of us - is that there are many places along this slow developmental path at which an incipient cancer can be stopped. Indeed, researchers have pinpointed some of the genes involved and they're working on treatments targeted directly at those genes.

more Stages of cancerous tumour. development.

Understanding how to stop the cancer, however, doesn't necessarily tell us how it starts.

Cells often react in unexpected ways to radiation, notes Dicello. For example, there's a puzzling phenomenon known as adaptive response. Sometimes, when tissue is exposed to damaging radiation, it not only repairs itself, but also learns to repair itself better next time. How that works is still being investigated.