For example, in one case a Baltimore County firefighter who retired in his mid-50s because of heart disease received $520,000 over 10 years — $226,000 in pension payments and $294,000 for heart damage caused by job stress, said Assistant County Attorney Suzanne Berger.

"In one select class of employees, we're paying twice as much," she said.

By contrast, she said, a police officer who retires with an accidental-disability benefit after being shot on duty would get a pension — typically 50 percent of preretirement earnings — but no workers' compensation payments because they're offset by the disability benefits.

Mixed research findings

Kerr and others say the cancer presumptions should be revisited and possibly curtailed because of new research findings. A National Institute for Occupational Safety and Health study of firefighters in three U.S. cities over six decades found no statistical link between the job and most of the cancers in Maryland's law, including breast cancer.

"I just want the medical science to make sense. If the science is there, I'm fine with it," Kerr said.

But firefighters and the law's other backers counter that the NIOSH study is only the latest in a line of sometimes-conflicting research.

"I wouldn't make any dramatic changes based on this study," said Dr. Virginia Weaver of the Johns Hopkins Bloomberg School of Public Health.

As director of Hopkins' occupational and environmental medicine residency program, Weaver trains doctors to determine causation in possibly job-related diseases. She said she supports presumption laws and noted that her students do a rotation at the International Association of Fire Fighters.

The science behind such legal presumptions is unsettled — and sometimes conflicting.

In 2012, when Maryland lawmakers weighed adding breast cancer and four other cancers to state law, they looked to a University of Cincinnati study that analyzed 30 previous research papers evaluating links between firefighters and cancer.

That "meta-analysis" concluded that brain and testicular cancers were a "possible" risk for firefighters, while non-Hodgkin lymphoma and multiple myeloma, the two blood cancers added to the law, were "probable." The study did not report any findings on breast cancer.

The General Assembly voted to add those five, while removing pancreatic cancer because of research findings. Counting the four cancers already on the books, that raised the total to nine.

Although most state laws take effect within months of passage, implementation of the law was delayed until June 2013 to give the state time to hire an expert for a new study of cancer risks for firefighters.

But the study never happened. The Professional Fire Fighters of Maryland objected to one expert identified by the state after learning he had testified in court that he believed presumptions lacked scientific basis. That expert withdrew, citing personal reasons.

During the 2013 General Assembly session, efforts to delay the new parts of the law failed, and the provisions took effect June 1 — without any new study.

Sen. Allan Kittleman, a Howard County Republican who represents employers as a workers' compensation lawyer in private practice, voted against the expansion, saying it had not sufficiently been studied. "You want to be fair with firefighters," he said, but the benefits should be "rational and reasonable, and not just because we like them."

Rund, the union leader, argued against delaying the new presumptions. In a February 2013 letter to Gov. Martin O'Malley, he urged all sides to give "serious consideration" to the NIOSH study when it came out, saying lawmakers could then make any needed changes to the law.

The NIOSH study, published in October, examined cancer rates among 30,000 firefighters in San Francisco, Chicago and Philadelphia between 1950 and 2009; it was five to six times larger than any previous study of its kind, according to researcher Dr. Robert Daniels.

Overall, the analysis found that firefighters may be at higher risk of digestive, oral, respiratory and urinary system cancers, he said. But of the nine cancers in Maryland law, only throat cancer had an elevated level that was statistically significant. The other cancers either did not show increased levels or the increases weren't deemed statistically significant given the small number of cases.