The deaths of four Ground Zero first responders from cancer and leukemia in recent days underscore the need for Congress to extend medical benefits for those who worked on the pile and later got sick, the head of an FDNY firefighters union said Thursday.

"We were domestic soldiers on that day when America was brought to its knees," said James Lemonda, president of the Uniformed Fire Officers Association Local 854 at a news conference in Manhattan to update the list of firefighters who have died or become ill since the Sept. 11, 2001, attacks.

Lemonda vowed to push Washington, D.C., legislators to extend the James Zadroga 9/11 Health and Compensation Act beyond its expiration date in 2016. The act provides medical treatment and health insurance coverage to first responders who cleared debris and searched for victims at Ground Zero amid toxic dust and fumes from the smoldering rubble.

"We will be asking elected officials in Washington to put aside their bipartisan politics and remember those who helped America on that day," Lemonda said.

Since the attacks, 92 members of the firefighter association have died and 875 have been diagnosed with 9/11-linked illnesses, union officials said. Of those diagnosed, 80 members' illnesses are at the critical stage and 177 are in remission, they said. Another 280 members are in the early stages of their illnesses and 25 are being tested to confirm whether their work at the World Trade Center is linked to them getting sick, according the union leaders.

On Saturday, retired FDNY Lt. John Gremse of Long Beach was buried after losing his battle with colon cancer. Gremse, who grew up in Valley Stream, was 64.

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"His prognosis was good, but in May the cancer spread to his mouth and liver," said his longtime friend Deputy Chief Paul Ferro of Division 13 in Queens.

Ferro described Gremse as "as an avid softball player, swimmer and surfer."

Two days later, three FDNY firefighters died. Esophageal cancer took the life of retired firefighter Daniel Heglund, 58, of Rocky Point, according to union officials. He was a member of Rescue 4 Ladder 33 in Woodside, Queens.

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Firefighter Robert E. Leaver, 56, of Engine Company 202 in Bay Ridge, Brooklyn, died of leukemia Monday. Retired Lt. Howard Bischoff, 58, of Ladder 149 in Brooklyn died of colon cancer.

Lemonda said the deaths have shaken association members "concerned as to what is going to happen to them in the future."