Higher rates of certain cancers have been documented among firefighters who responded to the 9/11 attacks on the World Trade Center (WTC). A recent study by researchers at Montefiore Medical Center in New York, however, found no significantly increased incidence of prostate cancer among firefighters exposed to the toxins released by the collapse of the Twin Towers compared to firefighters working in other U.S. cities.
But the study, which spanned September 2001 through December 2009, did see a rising rate of prostate cancers among the responding firefighters— between 2005-09, it was 1.4 times higher than in firefighters from other urban areas — suggesting that as the normal latency period for certain cancers draws to close, these observations may change.
The study, “Post-9/11 cancer incidence in World Trade Center-exposed New York City firefighters as compared to a pooled cohort of firefighters from San Francisco, Chicago and Philadelphia (9/11/2001-2009),” was published in the American Journal of Industrial Medicine.
During rescue and recovery efforts at the WTC, more than 13,000 firefighters with the City of New York (FDNY), and thousands of other responders, were exposed to potentially harmful substances. These included asbestos and polychlorinated biphenyls, both of which are classified as carcinogenic to humans by the International Agency for Research on Cancer.
“Specifically, bladder, gastrointestinal, liver, lung, prostate, melanoma, mesothelioma, and non-Hodgkin lymphoma have been found to be related to some or many of the substances found at the WTC site,” William Moir, MPH, the study’s first author, and colleagues wrote.
In a previous study, researchers reported a 10 percent increase in the rates of all cancers combined among these New York firefighters compared to the general U.S. population. Prostate and thyroid cancer, in particular, showed the highest levels of association with exposure to toxins at the WTC site.
At the time, however, researchers did not account for the impact of firefighting on a person’s cancer risk. A recent study evaluating 29,993 professional firefighters from three densely populated cities (San Francisco, Chicago, and Philadelphia) also showed increased incidence of all cancers combined, and particularly in digestive and respiratory cancers, as well as for mesothelioma.
In this study, investigators compared post-9/11 cancer incidence rates in WTC-exposed firefighters to those observed in cohorts of firefighters from San Francisco, Chicago, and Philadelphia who were not exposed at the WTC site.
Results revealed that exposed firefighters had similar cancer incidence rates to those observed in the non-exposed firefighters — except for thyroid cancer, which was four times higher in firefighters who served at the WTC site. But when the researchers accounted for the increased surveillance given the WTC firefighters, this increase was no longer significant.
Overall rates of prostate cancer were not seen to differ between the two firefighting groups. But when the research team compared incidence rates in the early (2001 to 2004) and later (2005 to 2009) post-9/11 periods, they found significantly higher rates of (1.4-fold) of this cancer in WTC-exposed firefighters.
This suggests that in cancers with longer latency periods, cancer incidence increases with time in WTC-exposed firefighters, and longer follow-up periods are needed to assess the relationship between toxin exposure among responders and cancer development. Latency period is the time a certain cancer usually takes to develop after exposure to something that can cause the disease.
“The main limitation of this study is the short follow-up period. Follow-up data for the referent group [non-WTC-exposed] of US firefighters ended in 2009, which limited the follow-up period for this study to only 8 years,” the researchers wrote. “Given that most cancers are believed to have relatively long latency periods, it is possible that the effects of WTC-exposure on cancer incidence would not manifest until the later part of our study period, or even until after it.”