No overall increased cancer risk for those exposed to WTC site

A new study has some good news for people who lived or worked in lower Manhattan after the Sept. 11, 2001, terrorist attack on the World Trade Center – exposure to dust and debris from the fallen twin towers has not resulted in an overall increased incidence of cancer.

The report, released Tuesday by the Journal of the American Medical Assn., is based on data from 55,778 people who are being tracked by the World Trade Center Health Registry, which includes first responders, people who worked or volunteered at the site during the recovery period, and those who lived, worked or attended school in the area. These people were exposed to several known and suspected carcinogens, including “asbestos, silica, benzene, polychlorinated biphenyls, polycyclic aromatic hydrocarbons, volatile organic compounds and numerous metals,” according to the study.

There’s plenty of reason to suspect that people who spent a lot of time near ground zero might be facing health risks. A study published last year in the Lancet found that among 9,853 male New York City firefighters, the incidence of all types of cancers was 19% higher among those who worked at the World Trade Center site than it was among those who weren’t first responders on the day of the attack. The men with “extra” cancers were diagnosed with prostate and thyroid cancers, non-Hodgkin’s lymphoma and melanoma.

For the new study, researchers from the New York City Department of Public Health and Mental Hygiene, the New York State Department of Health and colleagues looked at data collected through Dec. 31, 2008. There were 1,187 cases of cancer reported among the study participants being tracked by the health registry.

A little more than one-third (37%) of the cancer cases were diagnosed among people who were involved in the rescue and recovery operations, with the rest being found in people who lived or worked in lower Manhattan. In both groups, those with cancer were more likely to be older, to have a history of smoking, and to have had other medical problems than their counterparts who did not develop cancer.

Drilling deeper, the researchers compared some of the people in the study group with matched controls who were not exposed to the WTC site.

The overall cancer incidence among rescue and recovery workers was the same as with the controls. But zeroing in on cancers that appeared at least five years after the attacks – given the long latency period for cancer, these cases were more likely to be linked to WTC exposure – the researchers found that rescue and recovery workers were 43% more likely to develop prostate cancer, twice as likely to get thyroid cancer and nearly three times more likely to be diagnosed with multiple myeloma.

When the researchers used additional statistical controls to account for the fact that firefighters were more likely to get annual cancer screenings, the increased rate of thyroid cancer was no longer significant.

It’s not clear why these particular types of cancer would be more likely to arise. Thyroid cancer, for instance, can be caused by high exposure to ionizing radiation, but there’s no evidence that the WTC had unusual radiation levels. There are so many possible causes of prostate cancer that any connection would be hard to make, and previous studies have already found that firefighters have an increased risk of multiple myeloma even in the absence of an attack like this.

Despite the exposure to asbestos, no cases of mesothelioma were found.

Among the people who lived, worked or attended school in lower Manhattan, the risk of developing cancer of any sort was the same as for their matched controls who were not exposed to the WTC site. Two types of cancer were more likely to strike lower Manhattanites in the first five years after the attack – Hodgkin’s lymphoma and colorectal cancer – but since cancers take years to develop, it’s not clear whether those extra cases could be related to their proximity to the fallen twin towers. After five years, there were no types of cancer that were more likely to strike people who spent time in lower Manhattan.

The study authors also found that people who spent more time at the site – and thus would have greater exposure to anything harmful – were no more likely to develop cancer than people who spent less time there.

“In this early study with less than 8 years of follow-up, there was no statistically significant increased incidence for all cancer sites combined,” the researchers concluded. But that doesn’t mean everyone is out of the woods. Lung cancer, in particular, is known to have a long latency period, so it will “remain a concern given WTC exposure to asbestos, silica, and other carcinogens,” they wrote.

You can read the full study online here.

For more on the health issues facing people who lived or worked near the World Trade Center in the fall of 2001, check out this story from the Health section that ran near the 10th anniversary of the attack.

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