In a major blow for House Democrats — and a third dose of bad news in recent days for Democrats in New York — freshman Rep. Eric Massa (D) announced Wednesday that he would not seek re-election.

Massa’s seat, which Republicans were already targeting, becomes an even bigger pickup opportunity for the GOP. And the circumstances surrounding his departure may also provide talking points for the Republicans.

In a conference call with reporters, Massa, who is just 50 years old, cited a recurrence of cancer as the reason for his retirement. He angrily denounced “unsubstantiated” reports that he was being investigated by the House ethics committee.

Massa was diagnosed with a terminal form of lymphoma in 2001 and was forced to end his career in the Navy, which had culminated in a stint as top aide to Gen. Wesley Clark when Clark was supreme commander of NATO.

But his miraculous recovery helped inspire Massa to enter politics.

On Wednesday, he said he was hospitalized in December with a recurrence of cancer and that doctors told him he would need to get more rest.

“I run at about a hundred miles an hour. And my doctors have made it clear to me that I can no longer do that,” Massa said.

In a brief conversation Wednesday with the Web site Talking Points Memo, Massa conceded that he withheld the news of his hospitalization from his staff at the time.

But Politico reported earlier in the day that the House ethics committee had been alerted to a sexual harassment allegation against the freshman Congressman.

Massa did not directly address the allegations and did not take questions from reporters during the conference call. But he acknowledged that “I’m a salty guy” who has “used salty language” with staff, particularly when angry and in private. Massa said he has apologized to anyone he has offended. But he said “those kinds of articles — unsubstantiated without fact or backing — are a symptom of what’s wrong with this city.”

Former Corning Mayor Tom Reed (R), whom national Republicans had recruited to challenge Massa, said he was “saddened” to hear about Massa’s health problems.

“While the Congressman and I disagreed on political issues, I respect his military and public service and wish him the best,” Reed said in a statement.

But other Republicans weren’t so charitable. In a statement, New York GOP Chairman Ed Cox — the son-in-law of former President Richard Nixon — made note of the allegations in Politico and also sought to tie Massa to embattled Rep. Charlie Rangel (D-N.Y.) and scandal-plagued Gov. David Paterson (D), both of whom have been rocked by waves of bad news in recent days.

“Like so many other New York Democrats, his personal and professional behavior has left Massa scrambling for self-preservation rather than focused on public service. … With each passing day it appears New York Democrats are being consumed by a culture of corruption to the point where every New Yorker must question their ability to govern,” Cox said.

Ironically, Massa prospered politically in part because of the whiff of scandal surrounding the man he ousted last cycle, then-Rep. Randy Kuhl (R-N.Y.). When Kuhl was first running for the seat in 2004, details of a prior drunken driving arrest and his messy divorce became public — including testimony that he had threatened his ex-wife with two shotguns — and Kuhl never really regained his political footing, even though he won two House terms (defeating Massa by 3 points in 2006).

Kuhl on Wednesday night hinted that he might run for his old seat, but he mostly sent best wishes to Massa in a two-paragraph statement.

The 29th district, which runs from the suburbs of Rochester south to the Pennsylvania border, is one of the most conservative in New York. Even as Massa was defeating Kuhl by 2 points in 2008, Republican Sen. John McCain (Ariz.) was beating Barack Obama by 2 points in the presidential race.

Both parties were girding for a tough fight between Massa and Reed. But with Massa out of the picture, the political terrain could shift some more. While national Republicans saw Reed as a credible challenger, and Reed said Wednesday that local GOP leaders “all have pledged continued support for our campaign,” it is possible that bigger-name Republicans may step forward to run for the seat. Monroe County Executive Maggie Brooks (R) told media outlets in New York on Wednesday that she has been encouraged to look at the race and is considering it.

Monroe County voters make up about a third of the district, and it is one of the most Democratic parts of the district, so Brooks would start with several advantages. State Assembly Minority Leader Brian Kolb (R) and state Sens. Cathy Young (R) and George Winner (R) are also possibilities.

As of Dec. 31, Reed had $123,000 in his campaign account — hardly a sum that would keep bigger GOP names out of the race.

But with control of the state Senate a major battle point in New York this November, Republican leaders will be reluctant to see their Senate incumbents run for higher office unless they are convinced that the GOP can hold those seats.

“Does [the Massa vacancy] create a cascading effect that creates competitive races down the ballot?” said Evan Stavisky, a Democratic consultant and lobbyist in New York.

Meanwhile, Democrats must scramble to find a competitive candidate to replace Massa on the ballot. He is the 15th Democrat to announce plans to leave the House at the end of this year — and many sit in competitive districts that Republicans have a shot of flipping.

Democratic officials said Wednesday that state Assemblyman David Koon has begun making calls about the possibility of running for the Congressional seat. Koon was first elected to the Assembly in 1996, and he has a compelling personal story: His daughter was abducted and murdered before he entered politics, and Koon became politically active as an advocate for crime victims and children’s safety.

Hornell Mayor Shawn Hogan is also mentioned as a possible Democratic contender.

Paul Singer and Greg Giroux contributed to this report.