Rescue and recovery workers who provided aid after the World Trade Center attacks may have an increased risk of certain types of cancer, including prostate and thyroid cancers, a new study suggests.

However, that finding was based on a relatively small number of cancers. So there is no clear link. And neither relief workers nor people who lived, worked or went to school near the towers had a higher-than-average chance of being diagnosed with all cancers combined up to seven years later. The study was the largest to date, with 55,700 people.

"There's a lot of interest in the question of, does exposure to the World Trade Center cause cancer?" said Dr. Thomas Farley, the New York City Health Commissioner.

Based on this study, Farley said the role of the attacks on cancer risk is "complicated."

"Most of the people who have had cancer so far would have had it anyway," Farley told Reuters Health.

But because cancer can take 20 or more years to develop, the true risks may not become clear for many years, he added.

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