Firefighters who survived the 9/11 World Trade Center disaster were at least 19% more likely to develop cancer in the ensuing seven years compared to colleagues who were not exposed to the toxic cloud produced by the collapse of the twin towers, according to an observational cohort study published in a special Sept 3 issue of The Lancet that reflects on the health consequences of the terrorist attacks both in the US and internationally.

In the largest study of firefighters ever to be carried out, the researchers also found that the exposed firefighters were 10% more likely to develop cancer than a similar sample from the population at large.

The terrorist attacks on 11 September 2001 were the deadliest in the US since the second World War. The disastrous events that unfolded in New York City, Virginia, and Pennsylvania that day marked a new chapter in American and world history and have left a lasting imprint in the physical and mental health of the people affected.

The attacks on the World Trade Center (WTC) twin towers created an unprecedented environmental disaster where many first responders, including about 12,500 firefighters from the Fire Department of the City of New York (FDNY), were exposed to a toxic cloud containing many potentially hazardous substances including pulverized cement, lead, asbestos, glass fibers, polychlorinated biphenyls, polycyclic aromatic hydrocarbons, and byproducts of fires that broke out in the collapsed buildings such as polychlorinated furans and dioxins. This is in addition to toxic fumes from the burning jet fuel and from diesel exhausts from the heavy equipment used in the 10 months recovery effort following the attacks.

Senior author Dr David Prezant, professor of medicine at Albert Einstein College of Medicine of Yeshiva University, and colleagues, report how they evaluated the health of 9,853 WTC-exposed and non-exposed firefighters over the seven years following that day.

Prezant is also an attending physician in the pulmonary medicine division at Montefiore, the University Hospital and academic medical center for Einstein, and he is chief medical officer of the FDNY. His fellow co-authors are also from Einstein, Montefiore and FDNY.

Prezant has already published a number of papers on the lung health of the responders who attended the WTC disaster, but this latest study in The Lancet is the first to assess the rate of cancer in the entire cohort of WTC-exposed firefighters.

For the study, the authors examined the health records of all the firefighters participating in the research, dating back to 1996, five years before the WTC attacks.

They looked at cancer incidence and any potential links to exposure in the 7 years after 9/11. They compared these rates to those of firefighters who were not exposed to the WTC events, and also with a sample of the general population taken from the US National Cancer Institute’s Surveillance Epidemiology and End Results (SEER) database and matched for age, race and ethnicity of the firefighter cohort. They found that:

  • Compared with a matched sample of the general male population of the US, the standardized incidence ratios (SIRs) of the cancer incidence in firefighters exposed to the WTC events was 1.10 (95% Confidence Interval CI ranging from 0.98 to 1.25).

  • When compared with firefighters who were not exposed to the WTC events, the SIR of cancer incidence in the exposed firefighters was 1.19 (95% CI 0.96-1.47), when corrected for possible surveillance bias. When not corrected for bias, this was 1.32 (1.07-1.62). These figures were based on an excess of 38 cancer cases among the exposed firefighters.

The authors concluded that the results should be regarded with caution, because 7 years is not long enough to assess cancer outcomes, and the reported excess of cancer cases is “not limited to specific organ types”.

Also, as with all observational studies, where a group of people is followed over a period of time, you can’t rule out the possibility that the links they found might be due unidentified confounders.

Prezant told the press that the results:

“… support the need to continue monitoring firefighters and others who responded to the World Trade Center disaster or participated in recovery and cleanup at the site. This monitoring should include cancer screening and efforts to prevent cancer from developing in exposed individuals.”

The researchers also looked at the differences between exposed and non-exposed firefighters in terms of cancer occurring in 15 specific parts of the body, but found no site where there was a significant increase in cancer rates among those who were exposed to the WTC events.

However, they did see a trend toward increased risk in 10 of the 15 sites, and note that lack of statistical significance could be due to the small sample sizes for the site-specific analysis.

Small sample size was also a problem in analyzing for smoking status differences, although the authors note that all nine firefighters exposed to the WTC events who developed lung cancer were smokers.

The researchers believe that it is “biologically plausible” that exposure to the dust created by the WTC events can lead to cancer, although clearly this study does not prove any such link. The dust contained many known carcinogens, and also, exposure to the dust caused chronic inflammation, which has been ” implicated as a risk factor for cancer in experimental and epidemiological studies,” said Prezant.

The study was funded by the National Institute for Occupational Safety and Health (NIOSH).

Written by Catharine Paddock PhD