Fukushima, Japan: Even if the worst nuclear accident in 25 years leads to many people developing cancer, we may never find out.

Looking back on those early days of radiation horror, that may sound implausible. But the ordinary rate of cancer is so high, and our understanding of the effects of radiation exposure so limited, that any increase in cases from the Fukushima nuclear plant disaster may be undetectable.

Several experts inside and outside Japan told Agencies that cancers caused by the radiation may be too few to show up in large population studies, like the long-term survey just getting under way in Fukushima.

That could mean thousands of cancers under the radar in a study of millions of people, or it could be virtually none. Some of the dozen experts the AP interviewed said they believe radiation doses most Japanese people have gotten fall in a "low-dose" range, where the effect on cancer remains unclear.

The cancer risk may be absent, or just too small to detect, said Dr. Fred Mettler, a radiologist who led an international study of health effects from the 1986 Chernobyl disaster.

That's partly because cancer is one of the top killers of people in industrialized nations. Odds are high that if you live long enough, you will die of cancer.

The average lifetime cancer risk is about 40 percent. In any case, the 2 million residents of Fukushima Prefecture, targeted in the new, 30-year survey, probably got too little radiation to have a noticeable effect on cancer rates, said Seiji Yasumura of the state-run Fukushima Medical University.