Fifteen years have passed since the September 11 attack on the World Trade Center (WTC) in New York City (NYC), which not only killed and injured thousands of people but also exposed first responders and city residents to airborne toxins.
The health impact of exposure to these hazardous substances and the long-lasting effects of the trauma are now examined in a special issue of the American Journal of Industrial Medicine.
Two of the papers focus specifically on cancer risk.
One paper examined the cancer incidence in rescue/recovery workers (RRWs) as well as residents of lower Manhattan who were exposed to the dust and debris following the collapse of the WTC office towers. The authors conclude that there is some evidence of increased risk for cancer among exposed individuals and found that prostate cancer and cutaneous melanoma were significantly elevated in both populations.
The other study approached the issue from a different angle and specifically examined cancer occurrence in firefighters. But instead of comparing the cancer incidence in firefighters to that in the general population, the authors used a cohort of non-WTC-exposed firefighters.
This study found that the all-cancer incidence rate among the WTC-exposed firefighters was similar to that of the reference group of urban US firefighters.
However, the incidence of thyroid cancer was elevated over the entire study period, as was prostate cancer during the latter period. The authors note that these higher rates may be due in part to increased detection in the cohort from the Fire Department of the City of New York (FDNY).
Cancer Risk Debated
More than 13,000 career firefighters employed by the FDNY and tens of thousands of other individuals were exposed to a large array of potentially harmful substances resulting from tons of dust from the collapse of the buildings, along with combustion products from the fires that burned for several months following the attacks.
These substances included pulverized cement, glass fibers, asbestos, polybrominated diphenyl ethers, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, and polychlorinated furans and dioxins, some of which are classified as or are probably carcinogens.
As previously reported by Medscape Medical News, several studies have already suggested, to varying degrees, an increase in cancer risk among exposed individuals. In 2011, The Lancet reported that exposed firefighters had a higher risk for cancer compared with a similar demographic mix of the male population as well as to nonexposed New York firefighters.
A paper published a year later in JAMA reported small increases in rates of prostate and thyroid cancers and multiple myeloma in rescue and recovery workers beginning 6 years after 9/11.
In 2014, the FDNY released its own set of numbers for both fire fighters and emergency medical services (EMS) personnel.
Cancer Risk Higher in Responders/Residents
In the first of the just-published papers, a team of researchers led Jiehui Li, MBBS, MS, New York City Department of Health and Mental Hygiene, examined cancer incidence from 2007 to 2011 among 59,358 individuals: 24,170 RRWs and 35,188 non-RRWs (local residents, area workers, and school staff/students).
Overall, they observed a statistically significant excess incidence of total cancers among both workers engaged in rescue/recovery operations between September 11, 2001, and July 31, 2002 and non-RRW survivors.
Among RRWs, 685 first primary incident cancer cases were identified during 2007 to 2011. Cancer incidence was higher for 24 cancer sites combined and significantly differed from incidence in the reference population (adjusted standardized incidence ratio [SIR], 1.11).
The incidence of prostate cancer (number of observed cases, 223; SIR, 1.43), thyroid cancer (number of observed cases, 37; SIR, 1.79), and skin melanoma (number of observed cases, 37; SIR, 1.49) was significantly increased.
Of note, the SIR for lung cancer was significantly reduced during this period (number of observed cases, 42; SIR, 0.69), and 1 mesothelioma case was reported. Among the non-RRW population, 992 first primary incident cancer cases were identified (SIR, 1.08). Of the 24 cancer sites, the incidence in 4 was significantly elevated: prostate (number of observed cases, 196; SIR, 1.27), skin melanoma (number of observed cases, 44; SIR, 1.54), female breast (number of observed cases, 187; SIR, 1.34), and non-Hodgkin's lymphoma (number of observed cases, 56; SIR, 1.49).
As with rescue workers, there was also a significantly reduced SIR for lung cancer (number of observed cases, 67; SIR, 0.69); 1 mesothelioma case was reported.
Dr Li and colleagues concluded that the excess incidence of prostate and thyroid cancers has continued among RRWs, but a small and statistically higher than expected rate was seen for melanoma in both groups and for female breast cancer and non-Hodgkin's lymphoma among non-RRWs.
They also point out that the "increased incidence in most of these cancers lacked support from internal comparisons to examine whether there was an association with magnitude of exposure."
For example, despite a significant dose-response trend associated with melanoma among the civilian population, the absence of information on ultraviolet-light exposure before and after 9/11 (a major confounder) "makes meaningful interpretation of causality between WTC exposure and the cancer difficult," they note.
But despite these limitations, "our findings show some evidence of increased risk of cancer among WTC exposed populations, yet they need to be substantiated by additional follow-up studies as the latency period from a potential WTC exposure increases," the authors write.
Firefighter vs Firefighter
In the second study, William Moir, MPH, from Montefiore Medical Center and the FDNY, and colleagues compared firefighters exposed to WTC toxins (n = 11,457 white male firefighters) to a cohort of non-WTC-exposed firefighters from other urban areas (San Francisco, Chicago, and Philadelphia; n = 8220 white male firefighters).
A total of 345 individuals from the FDNY cohort and 443 individuals from the referent group were diagnosed with a first primary cancer from September 11, 2001, to December 31, 2009.
The researchers found no significant difference in the overall cancer rate between the WTC-exposed firefighters and the reference group (relative rate [RR], 0.96).
But among firefighters aged 35 to 60 years in the exposed group, thyroid cancer was significantly elevated (RR, 3.82). There were insufficient cases in other age groups to permit determination of risk.
The rate of lung cancer was lower for the FDNY exposed group among men aged 45 to 70 years (RR, 0.55), and no significant differences were observed for other types of cancer, including colon, prostate, and hematologic cancers and melanoma.
A secondary analysis that compared early and late post-9/11 periods showed results similar to those of the primary analysis. The incidence of thyroid cancer was elevated during the entire study period, while prostate cancer incidence rose during the late period (RR, 1.38).
"However, the elevated rates may be due in part to increased detection in the FDNY cohort," the study authors note.
"Further follow-up should be conducted with this reference population to assess the relationship between WTC-exposure and cancers with longer latency periods and aim to control for potential confounders such as smoking," they conclude.
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