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. 2011 Sep 3;378(9794):898-905.
doi: 10.1016/S0140-6736(11)60989-6.

Early assessment of cancer outcomes in New York City firefighters after the 9/11 attacks: an observational cohort study

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Early assessment of cancer outcomes in New York City firefighters after the 9/11 attacks: an observational cohort study

Rachel Zeig-Owens et al. Lancet. .

Abstract

Background: The attacks on the World Trade Center (WTC) on Sept 11, 2001 (9/11) created the potential for occupational exposure to known and suspected carcinogens. We examined cancer incidence and its potential association with exposure in the first 7 years after 9/11 in firefighters with health information before 9/11 and minimal loss to follow-up.

Methods: We assessed 9853 men who were employed as firefighters on Jan 1, 1996. On and after 9/11, person-time for 8927 firefighters was classified as WTC-exposed; all person-time before 9/11, and person-time after 9/11 for 926 non-WTC-exposed firefighters, was classified as non-WTC exposed. Cancer cases were confirmed by matches with state tumour registries or through appropriate documentation. We estimated the ratio of incidence rates in WTC-exposed firefighters to non-exposed firefighters, adjusted for age, race and ethnic origin, and secular trends, with the US National Cancer Institute Surveillance Epidemiology and End Results (SEER) reference population. CIs were estimated with overdispersed Poisson models. Additional analyses included corrections for potential surveillance bias and modified cohort inclusion criteria.

Findings: Compared with the general male population in the USA with a similar demographic mix, the standardised incidence ratios (SIRs) of the cancer incidence in WTC-exposed firefighters was 1·10 (95% CI 0·98-1·25). When compared with non-exposed firefighters, the SIR of cancer incidence in WTC-exposed firefighters was 1·19 (95% CI 0·96-1·47) corrected for possible surveillance bias and 1·32 (1·07-1·62) without correction for surveillance bias. Secondary analyses showed similar effect sizes.

Interpretation: We reported a modest excess of cancer cases in the WTC-exposed cohort. We remain cautious in our interpretation of this finding because the time since 9/11 is short for cancer outcomes, and the reported excess of cancers is not limited to specific organ types. As in any observational study, we cannot rule out the possibility that effects in the exposed group might be due to unidentified confounders. Continued follow-up will be important and should include cancer screening and prevention strategies.

Funding: National Institute for Occupational Safety and Health.

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Conflict of interest statement

Conflicts of interest

We declare that we have no conflicts of interest.

Figures

Figure
Figure. Primary and secondary analyses displaying point estimates and 95% CIs for all cancer sites combined
Primary cohort (corrected after 2008 incident cancers): standardised incidence ratios (SIRs) ratio of first cancers in World Trade Center (WTC) exposed firefighters versus non-exposed firefighters. Corrected incident cancers: SIR ratio of first cancers in exposed versus non-exposed firefighters, with the diagnosis date delayed by 2 years for 25 cases, which might have been detected by FDNY screening. Corrected after 2008 incident cancers: SIR ratio of first cancers in exposed versus non-exposed firefighters with diagnosis dates delayed to beyond 2008, the study period, for 25 cases that might have been detected by FDNY screening. Early period: SIR ratio of exposed firefighters in the early follow-up period (Sept 11, 2001 [9/11], to Dec 31, 2004) after 9/11, versus non-exposed firefighters. Late period: SIR ratio of exposed firefighters in the late follow-up period (Jan 1, 2005, to Dec, 31, 2008) after 9/11 versus non-exposed firefighters. Hazard ratio incident cases: ratio of hazard-ratio rates of first cancers in exposed firefighters versus non-exposed firefighters estimated with the Cox model. Multiple primary cancers: SIR ratio of multiple primary cancers in exposed firefighters versus non-exposed firefighters. Expanded cohort: SIR ratio of first cancers in exposed firefighters versus non-exposed firefighters including those who began employment between Jan 1, 1996, and Sept 10, 2001.

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