Cause and effect - nuclear or otherwise - is much harder to prove, but is possible, Mandel said. Thyroid cancer can be caused by radiation in two ways, she said: "internal" or ingested radiation, such as that from Chernobyl and other releases, and "external" radiation, passed through the skin from CAT scans.
Cancers from ingested radiation can be identified because they are more likely than the others to carry a specific genetic mutation, she said.
At the City Hall news conference, Mangano and others agreed that their data proved nothing. But some advocates said the questions alone should be enough to rethink nuclear power.