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Ongoing research funded by the World Trade Center (WTC) Health Program has continued to show associations between exposures to the WTC site after the terrorist attacks on Sept. 11, 2001 and various cancers, as evidenced by two studies recently published in Occupational & Environmental Medicine.

According to the first , male New York City firefighters exposed to the WTC site had higher rates of all cancers (relative rate [RR] 1.13, 95% CI 1.02-1.25) and a younger median age at diagnosis (55.6 vs 59.4 years) compared with male non-WTC-exposed firefighters.

Specifically, WTC-exposed firefighters had increased rates of prostate cancer (RR 1.39, 95% CI 1.19-1.63), thyroid cancer (RR 2.53, 95% CI 1.37-4.70), melanoma (RR 1.12, 95% CI 0.80-1.57), and non-Hodgkin lymphoma (RR 1.26, 95% CI 0.80-1.57), reported Mayris Webber, DrPH, of the Bureau of Health Services at the Fire Department of the City of New York, and colleagues.

The second from Charles Hall, PhD, of Albert Einstein College of Medicine in the Bronx, and colleagues, found that, beginning in 2007, rescue/recovery workers at the WTC site had a 24% increased risk for prostate cancer compared with the general population in New York State (HR 1.24, 95% CI 1.16-1.32).

In an accompanying , Geoffrey Calvert, MD, MPH, of the WTC Health Program, and colleagues highlighted the uniqueness and importance of their program, which has enrolled more than 110,000 members and "remains steadfast in its mission to provide high-quality healthcare to 9/11 responders and survivors."

"Medical treatment benefits are provided only for those conditions determined to be related scientifically to toxic agent exposures encountered by 9/11 responders and survivors," Calvert and co-authors wrote. "Cancer research findings among WTC responders and survivors were an important factor leading to the addition in 2012 of most cancer types to the list of covered conditions."

Excess Cancer Risk

According to Webber and colleagues, all firefighters are repeatedly exposed to occupational hazards, including known carcinogens. Their previous found no difference between WTC-exposed firefighters and a group of non-WTC-exposed firefighters from Philadelphia, Chicago, and San Francisco. The current study extended follow-up to allow for detection of cancers up to 15 years after WTC site exposure.

In this analysis of 10,786 WTC-exposed firefighters and 8,813 non-WTC-exposed firefighters, there were 915 incident cancer cases in 841 exposed men and 1,002 cases in 909 non-exposed men. Prostate cancer was the most commonly diagnosed cancer among both groups, followed by melanoma of the skin and non-Hodgkin lymphoma in the exposed group and lung cancer and melanoma in the non-exposed group.

Compared with the U.S. male population, all-cancer incidence among exposed firefighters was "higher than expected" (standardized incidence ratio 1.09, 95% CI 1.02-1.16), even after adjustment for possible surveillance bias.

Since WTC-exposed firefighters undergo free health monitoring exams without copays, allowing for possible earlier cancer detection, the researchers corrected for this by using a 2-year lag in diagnosis dates for certain cancers. This adjustment attenuated risk, but rates were still elevated for all cancers (surveillance adjusted RR 1.07), prostate cancer (surveillance adjusted RR 1.28), non-Hodgkin lymphoma (surveillance adjusted RR 1.21), and thyroid cancer (surveillance adjusted RR 2.11).

This adjustment for possible surveillance bias is a lesson that can be applied to research more broadly, and without which could "produce unreliable research findings," Calvert told MedPage Today.

"When the role of elevated cancer screening rates was taken into account, cancer risks were still elevated," he noted. "However, those 'adjusted' cancer risks were lower when compared to the cancer risks observed before cancer screening rates were taken into account."

Webber and colleagues acknowledged that assessment of cancer risk among WTC-exposed firefighters is complex, as "these firefighters were subject to carcinogenic exposures, while also enduring enormous physical and mental burdens related to the attacks."

"Evidence is slowly accruing about cancer and other long latency illnesses in relation to WTC exposure, although much remains to be determined," they added.

From Exposure to Diagnosis

Previous research in the field of prostate cancer has estimated that it can take 10 to 20 years from exposure to a carcinogen to cancer diagnosis. Although there is a known link between WTC exposure and prostate cancer among responders, the length of time between exposure and cancer diagnosis was unknown.

Among the 54,394 rescue/recovery workers included in the study by Hall and colleagues, there were 1,120 prostate cancer cases diagnosed from March 2002 to December 2015.

The median time from the attacks to a diagnosis was 9.4 years, with the majority (66%) of cases diagnosed from 2009 to 2015.

The researchers acknowledged that higher-than-general rates of prostate-specific antigen (PSA) screening among first responders could have played a role in the increased incidence of prostate cancer seen in the study.

Comparing the responders who arrived earliest to the site -- Sept. 11, 2001 or Sept. 12, 2001 -- with those who arrived later revealed a positive, monotonic, dose-response association with the early (2002-2006) and late (2007-2015) periods.

"The increased hazard among those who responded to the disaster earliest or were caught in the dust cloud suggests that a high intensity of exposure may have played some role in premature oncogenesis," Hall and colleagues wrote. "Our findings support the need for continued research evaluating the burden of prostate cancer in WTC responders."