Nearly a year after federal epidemiologists first sounded the alarm over a cluster of rare blood cancers in northeastern Pennsylvania, their research has zeroed in on a hardscrabble region 80 miles northwest of Philadelphia that is home to several Superfund sites and a power plant fired by waste coal.

The U.S. Agency for Toxic Substances and Disease Registry said Monday that it confirmed an elevated number of cases of polycythemia vera, or PV, in a 20-mile stretch between Hazleton and Tamaqua.

Researchers said they confirmed 33 cases of PV in Luzerne, Carbon and Schuylkill counties. That was a slightly lower number than they reported last October at the conclusion of their preliminary investigation into the cluster.

It remains the first and only cluster of PV ever recorded in the United States, though the condition became reportable to state cancer registries only in 2001, and officials said it's statistically likely there are others.

Residents in the affected area were four times as likely to suffer from PV as residents living in outlying areas, according to the government.

Researchers cautioned, though, that their investigation was not designed to uncover an environmental link to PV, a cancer that results in the overproduction of red blood cells and can lead to heart attack or stroke. PV's cause is unknown.

"We don't want to give the message that there are no connections," said researcher Vince Seaman. "We just don't have the data."

Some residents blame their illnesses on a recycler that accepted hundreds of thousands of gallons of paint sludge, waste oils, used solvents, PCBs, cyanide, pesticides and many other known or suspected carcinogens.

Environmental officials shut down the site in 1979, and it was later placed on the federal Superfund list and cleaned up. Other Superfund sites dot the area, too, along with a power plant that burns waste coal that some residents also suspect has caused health problems.

The agency revealed its latest findings at a community meeting in Hazleton on Monday night.

Researchers said they found that Pennsylvania does not accurately report the number of PV cases statewide. That's because the criteria for diagnosing the illness have changed and because PV is reported only by hospitals.

Seaman said inaccurate PV reporting is also likely a problem in other states.

U.S. Sen. Arlen Specter announced Monday that the Senate Appropriations Committee approved $262,000 for a planned Drexel University investigation into the cluster. The funding has yet to clear the full Senate.

"It is clear that more research is necessary to pinpoint the reasons for this cluster, including whether environmental contaminants are a factor," Specter said in a statement.