The study was by far the largest to date. It examined 55,700 people, including rescue and recovery workers at the World Trade Center site, on barges or at the Staten Island landfill where debris was taken, in the nine months after Sept. 11, 2001, as well as residents of lower Manhattan, students, workers and passers-by exposed on the day of the terrorist attacks.
Overall, there was no increase in the cancer rate of those studied compared with the rate of the general population, researchers concluded after looking at 23 cancers from 2003 to 2008. The prevalence of three cancers were significantly higher — multiple myeloma, prostate and thyroid — but only in rescue and recovery workers, and not in the rest of the exposed population.
And the researchers noted that those were very common cancers and that the number of people who received diagnoses of them was small. In one of many counterintuitive findings, the incidence of cancer was not higher among those who were more intensely exposed to the toxic substances than among those who were less exposed.
Given the lack of evidence of a link between the Sept. 11 debris and cancer, some epidemiologists had questioned the decision by the government in June to add 50 types of cancer to the list of illnesses covered by the James Zadroga 9/11 Health and Compensation Act, signed by President Barack Obama in early 2011. That decision to add cancer to the list meant that people with other sicknesses more strongly linked to ground zero were likely to receive less money.
Dr. Thomas A. Farley, the health commissioner in New York City, said in an interview Monday that it was too soon to take the study as a repudiation of the federal government's decision.
''Cancers take 20 years to develop," Farley said, "and we might see something different 20 years down the line." But echoing Dr. John Howard, head of the National Institute for Occupational Safety and Health, who made the final decision on covering cancer, the commissioner added, "You don't want to wait 20 to 30 years to get a definitive answer to which people may be suffering today."
Dr. Alfred I. Neugut, an oncologist and professor of epidemiology at the Mailman School of Public Health at Columbia University, said he was not surprised by the study. "I think, given the time frame and the exposures," he said, "that there wasn't a high likelihood that there would be an elevated risk, certainly for cancer, and to the degree that it was, it would not be for the cancers that they're finding."
Neugut said he sympathized with people who had cancer that they attributed to the disaster, but added that their emotional response was not necessarily scientifically valid. "The 9/11 attack was a terrible thing, but it doesn't cause everything in the world," he said. "Cancer is a very specific outcome, and in most exposures, you have to be exposed for an extended time before you get the cancer."
Initially, the money set aside by the law — $2.8 billion to compensate victims and $1.5 billion for monitoring and treatment costs not covered by health insurance — covered mainly respiratory illnesses. (Mental health problems were included in the treatment fund but not the compensation fund.) Studies by the city health department have found asthma and post-traumatic stress disorder to be linked to the 2001 attacks. But cancer is expected to be far more expensive to treat and, perhaps, to compensate, since many cancer patients cannot work or have died.
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The recent study was released Tuesday and was to be published in Wednesday's issue of The Journal of the American Medical Association — too late to influence Howard's decision, but perhaps not too late to influence public opinion going forward and to affect whether Congress will decide to replenish the victim compensation fund should more money be needed.
The fund has not yet begun making payments, and it is supposed to make its final payments in 2016-17. In the meantime, some police officers and other rescue and recovery workers who worked at ground zero and have cancer have been receiving enhanced pension benefits based on a 2005 state law that said they were presumed to have contracted cancer from the ground zero substances.
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Until now, the only systematic examination of cancer incidences and Sept. 11 was a study by the New York Fire Department that was released last year. It found a 19 percent higher incidence of all types of cancer for exposed firefighters compared with those not exposed. Most of the increase came from prostate and thyroid cancers, non-Hodgkin lymphoma and melanoma.
The health department study found a 43 percent higher risk of prostate cancer, double the risk of thyroid cancer, and nearly triple the risk of multiple myeloma, a blood cancer of the bone marrow, in rescue and recovery workers. But the researchers cautioned that it was too early to know if the increases were related to Sept. 11 and that the number of people affected was small — seven cases of myeloma, of which two or three would have been expected to occur based on the normal cancer rate, making it all but impossible to tell which were related to the attacks and which were not.
There were several confounding factors, including the likelihood that the rescue and recovery workers were more diligently screened for prostate and thyroid cancer than the population at large, and the absence of a correlation with the intensity of exposure.
''Cancer's always a bad thing," said Farley, the health commissioner. "But the prostate and thyroid cancer was no more common in people who were more exposed, which is something you would expect if it was caused by the disaster."
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Prostate and thyroid cancer also have different origins, the study said, with thyroid cancer caused by ionizing radiation — which is not believed to have been present in carcinogenic amounts at the World Trade Center site — and prostate cancer's relationship to environmental factors being inconclusive. On the other hand, blood cancers like myeloma tend to develop quicker than solid tumors and, therefore, could be an early indicator of cancer risk, the study said.
Part of Howard's rationale for adding cancer to the list of eligible illnesses was that the dust, smoke and fumes were known to contain potential carcinogens like asbestos, silica, benzene, polychlorinated biphenyls, polycyclic aromatic hydrocarbons, volatile organic compounds and metals.
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Patricia Workman, who volunteered at ground zero and has myeloma and melanoma, both on the federal list of qualifying cancers, said she was disappointed by the study's findings.
''It's like one thing comes out that's good, and then it's just a setback," said Workman, who has become an advocate for people with myeloma. She added that she had gone to the funerals of first responders who died of leukemia, and was surprised it was not one of the cancers the health department study linked to Sept. 11.
Workman suggested that the government might have unnecessarily invited criticism of the treatment and compensation program by covering so many types of cancer so soon.
''They gave too much away in the beginning to say every cancer was covered and everybody that was down there was covered," she said. "You've got to prove that it's linked to being down there. But I hope that people will speak up and fight."