WASHINGTON — Rep. Eric J.J. Massa, a Corning Democrat who is fighting off a possible recurrence of cancer and an accusation that he made an improper advance toward a male aide, said Friday he will resign from Congress, effective at 5 p.m. Monday.

In a long, emotional statement issued Friday afternoon, Massa acknowledged using language in his home and in his office "that, after 24 years in the Navy, might make a chief petty officer feel uncomfortable."

Given that he had used such inappropriate language, "in fact, there is no doubt that this ethics issue is my fault and mine alone," Massa said in his statement.

"But in the incredibly toxic atmosphere that is Washington, D.C., with the destruction of our elected leaders having become a blood sport, especially in talk radio and on the Internet, there is also no doubt that an ethics investigation would tear my family and my staff apart," he added.

That being the case, Massa said he will step down.

"I do so with a profound sense of failure and a deep apology to all those whom, for the past year, I tried to represent as our nation struggles with problems far greater than anyone can possibly imagine," said Massa, whose district encompasses much of the Southern Tier.

"I hope that my family, constituents, and fellow members of Congress can accept this apology as being both genuine and heartfelt, and I wish for them and all Americans only the best."

Two sources with knowledge of the situation told The Buffalo News on Thursday that a male staffer has accused Massa of making unwanted advances.

The sources, who asked not to be identified, confirmed that the staffer had complained about comments the congressman allegedly made that the aide perceived as sexually suggestive.

The House ethics committee issued a statement Thursday acknowledging it is "investigating and gathering additional information concerning matters related to allegations involving Rep. Massa."

Massa said in his statement Friday that he first learned about the ethics allegation against him from the Internet.

"After I decided not to run again, I was told, for the first time, that a member of my staff believed I had made statements that made him feel "uncomfortable,' " Massa said.

While citing a "major cancer recurrence scare" two days ago, Massa — a survivor of non-Hodgkin's lymphoma — was a bit more specific about his health in the statement he released Friday.

"Two days ago as I sat reading my new annual CAT scan, having been told that the anomalies in the films may or may not be scar tissue, I decided to finally take the advice that my doctors have repeatedly given me, and that is to take care of my family and myself before my profession," he said.

Earlier Friday, Joseph Racalto, Massa's chief of staff, said Massa's health had prevented him from voting during the House session Thursday.

"He is sick," Racalto said in a conversation several hours before he announced Massa's resignation. "He is missing votes because he is under his doctor's care."

Massa, 50, a retired Navy commander, has a wife and two children.

He was elected to Congress in 2008, defeating then-Rep. Randy Kuhl, a Hammondsport Republican, after losing a bid to unseat Kuhl two years earlier.

Ironically, Massa's resignation could help Democrats in one way: Massa opposed the party'shealth reform bill — and his departure lowers the number of votes needed for passage by one, to 216.

Todd Valentine, a spokesman for the state Board of Elections, said the governor could call a special election, but is not obligated to do so. Gov. David A. Paterson's office said it had no information about a special election.

Still, Valentine said governors usually schedule such contests when the vacancy occurs at this point in the calendar. He added that the winner would have to run again in November for a full two-year term.

The Republican nominee, to be chosen by the county party chairmen in the district, would be the overwhelming favorite for a special election, given the GOP's huge enrollment advantage in the district and the party's success in other elections across the country this year.

Monroe County Executive Maggie Brooks has expressed interest in the seat, and many GOP leaders expect her to emerge as the leading contender.

But former Corning Mayor Tom Reed has been running against Massa for months, and Kuhl has expressed interest in trying to regain his old seat.

"Although I am still deciding on my political future, one thing is for sure: We need a proven experienced leader to represent the 29th Congressional District," Kuhl said Friday.

Other possible Republican candidates include State Sens. George H. Winner Jr. of Elmira and Catharine M. Young of Olean, along with Assembly Minority Leader Brian M. Kolb of Canandaigua and Chemung County Executive Thomas J. Santulli.

Democrats mentioned include Assemblyman David Koon and Assemblywomen Susan V. John and Barbara Lifton of Monroe County, along with Hornell Mayor Shawn D. Hogan, who said Wednesday Massa had urged him to seek the seat.

News Staff Reporters Robert J. McCarthy and Tom Precious contributed to this report.