Today the air is clear and calm at the 9/11 Memorial in New York City, far from what it was on Sept. 11, 2001. After the World Trade Center fell, the air was filled with dust, debris and toxic emissions.

"We know that there were serious exposures to cancer causing agents from 9/11," said Dr. Steven D. Stellman of the New York City Department of Health and Mental Hygiene. "That's a serious public health concern."

The World Trade Center Health Registry has followed almost 56,000 survivors from 9/11. They were rescue and recovery workers, residents and visitors of Lower Manhattan at the time of the attack. The registry tracks their emotional and physical health, including cancer incidence compared to typical New York cancer rates.

"In both the rescue recovery workers and the non-rescue recovery workers, we did not find any different overall cancer rate from what we determined from the background rate from the New York state cancer registry," Stellman said.

In the study published in the Journal of the American Medical Association, they did find that rescue recovery workers had a significantly increased rate of three types of cancer – prostate, thyroid and myeloma, a blood cancer.

Researchers say rates for prostate and thyroid cancers were also elevated in a recent study involving New York firefighters.

Researchers say cancer is fundamentally different from many other 9/11-related diseases.

"Most solid tumors have a very long latency period," Stellman said. "Many don't appear for many years or decades after the initial exposure."

Researchers say certain types of cancers should continue to be tracked.