New data suggest an increased risk of leukemia among responders who worked at the World Trade Center site after the attacks on Sept. 11, 2001.
Courtesy Andrea Booher/FEMA News Photo
A New York firefighter digs through the rubble at Ground Zero while wearing a protective mask.
Previous studies have shown that 9/11 responders have a higher incidence of cancers than does the general population. The current study is the first to show a higher incidence of leukemia among responders. It also shows a higher incidence of thyroid and prostate cancers as well as all cancer types combined.
These findings were published in JNCI Cancer Spectrum.
“This study showed increased incidence of several cancer types compared to previously conducted studies with shorter follow-up periods,” study author Susan L, Teitelbaum, PhD, of the Icahn School of Medicine at Mount Sinai, New York, said in a press release.
“Because of the long latency period of many types of cancer, it is possible that increased rates of other cancers, as well as World Trade Center exposure health issues, may emerge after longer periods of study.”
Dr. Teitelbaum and colleagues evaluated responders enrolled in the World Trade Center Health Program General Responder Cohort from when it was established in July 2002 through the end of follow-up, which was Dec. 31, 2013, for New York residents and Dec. 31, 2012, for residents of other states.
To be eligible for the cohort, responders must have worked on the World Trade Center rescue and recovery effort a minimum of 4 hours in the first 4 days from Sept. 11, 2001, 24 hours in September 2001, or 80 hours from September through December 2001. Responders also had to complete at least one monitoring visit.
Responders’ data were linked to data from cancer registries in New York, New Jersey, Pennsylvania, and Connecticut (where most responders lived at the time of the attacks), as well as Florida and North Carolina (where responders were known to retire). The responders were linked to the registries using probabilistic matching algorithms, which made use of information such as patient name, address, social security number, sex, race, and birth date.
The researchers noted that patients who enrolled in the General Responder Cohort had their cancer certified for federally funded treatment, and this factor might result in “sicker members disproportionately self-selecting into the program.” To reduce this potential bias, the researchers conducted a restricted analysis in which counts of cancer cases and person-years of observation began 6 months after responder enrollment.
The researchers analyzed data on 28,729 responders who primarily worked in protective services (49.0%) and construction (20.8%). Responders spent a median of 52 days on the rescue and recovery effort, and 44.4% of them had some exposure to the dust cloud caused by the collapse of the towers.
In the restricted analysis, there were 1,072 cancers observed in 999 responders. Compared with the general population, responders had a significantly higher incidence of all cancers combined, with a standardized incidence ratio (SIR) of 1.09.
Responders had a significantly higher incidence of prostate cancer (SIR,1.25), thyroid cancer (SIR, 2.19), and leukemia (SIR, 1.41). The leukemia category included acute myeloid leukemia (SIR,1.58) and chronic lymphocytic leukemia (SIR, 1.08).
“Although other studies have revealed elevated SIRs for other hematologic malignancies, this is the first reported, statistically significant, elevated SIR for leukemia,” the researchers wrote. “Leukemia is known to occur after exposure to occupational carcinogens, including benzene (burning jet fuel and other sources at the [World Trade Center] site), possibly at low levels of exposure and with a latency of several years from exposure.”
A multivariate analysis showed no association between cancer incidence and the length of time responders spent on the rescue and recovery effort or the intensity of their exposure to the dust cloud or debris pile.
The analysis did show an elevated risk of all cancers combined with each 1-year increase in responder age (hazard ratio, 1.09), among male responders (HR, 1.21), and among responders who smoked at baseline (HR, 1.29).
This research was supported by the Centers for Disease Control and Prevention/National Institute for Occupational Safety and Health. The researchers disclosed no conflicts of interest.
SOURCE: Shapiro MZ et al. JNCI Cancer Spectr. 2020 Jan 14. doi: 10.1093/jncics/pkz090.