There's no clear evidence that the dust, debris and fumes released by the destruction of the World Trade Center in the September 11 attacks causes cancer, according to a new study from the New York City department of health.

Dr. Carolyn Green, a deputy commissioner at the health department who co-authored the study, says the findings are still very early and that her agency will continue investigating.

“We are going to continue to monitor trends over time. We’re going to continue to look at our registry of 71,000 people directly exposed to the world trade center disaster,” Dr. Green said.

Green says there is plenty of evidence that links the world trade center attacks with asthma and PTSD.