Dr. Neugut said he sympathized with people who had cancer they attributed to the disaster, but added that their emotional response was not necessarily valid scientifically. “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 than other qualifying illnesses, and the economic loss caused by cancer could require more compensation, since many cancer patients cannot work, and some have died.

The study was released on Tuesday, and was to be published in the Wednesday issue of The Journal of the American Medical Association — too late to influence Dr. Howard’s decision, but perhaps not too late to influence public opinion going forward or 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.

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 roughly 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, two or three of which would have been expected 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 13 cases of thyroid cancer, 7 more than expected, and 67 cases of prostate cancer, 20 more than expected.

Several factors made it hard to draw any conclusions from those results, including the possibility that the rescue and recovery workers were screened more routinely for prostate and thyroid cancer — a factor researchers call “surveillance bias” — than the population at large, and the absence of a correlation with the intensity of exposure.