It's the latest claim in a changing stream of explanations that have propelled him from a relatively obscure Democratic lawmaker to darling of conservative talk show hosts.
But his explanation leaves out a key fact: The decision and timing of his resignation were Massa's alone.
Massa could have stayed in Congress and cast votes on health care in the coming weeks even as he awaited the results of a House ethics panel probe into allegations he harassed a male staffer. Most lawmakers facing congressional ethics investigations remain in office.
Massa's charge on the health care vote struck a responsive chord with conservative bloggers and talk radio personalities who touted the former congressman's claims as proof of a win-at-all-costs approach by Democratic congressional leaders and the White House as they make a final push to pass a health care overhaul in Congress.
Massa, a freshman, was one of 39 Democrats who voted against an earlier version of the health care bill in November. His departure reduces the majority House Speaker Nancy Pelosi needs for passage of the legislation to 216 votes.
THE CLAIM: Massa says he was targeted by Democrats who will "stop at nothing" to advance their health care overhaul. On a New York radio station Sunday, Massa blamed Democrats for his downfall, saying, "I was set up for this from the very, very beginning."
THE FACTS: Massa was the one who decided to leave the House, and when. He has given four different reasons over the past week for resigning his seat, including health worries and the ethics probe.
He first announced last Wednesday that
Massa, 50, who was stricken with non-Hodgkin's lymphoma in 1996, said his cancer had returned in December. He dismissed a media report that he had been accused of sexually harassing a staffer. But he admitted to using "salty language" around his staff.
On Wednesday night, House Majority Leader Steny Hoyer said in a statement that a staff member in Massa's office told him about misconduct allegations Feb. 8. to the House ethics panel within 48 hours. Hoyer said he got confirmation within that time that the ethics panel had received the report and would review the allegations. Hoyer's statement came in response to reporters' questions.
On Thursday, the House ethics panel confirmed in a brief statement that it was "investigating and gathering additional information concerning matters related to allegations involving" Massa.
The next day, Massa announced he would resign his seat effective Monday. He cited the ethics probe, saying it "would tear my family and my staff apart." He called himself "a deeply flawed and imperfect person."
On Sunday, Massa went on a New York radio station and blamed Democrats for conspiring against him and forcing him out because he opposed their health care push. Democrats deny that, and Massa offered no evidence of tactics to force him out.
Massa, who is married, said the ethics complaint stems from a remark he made across a table of male staffers during a New Year's Eve wedding reception. When an aide suggested he should be chasing after a bridesmaid, Massa said he responded by making a sexual comment to another staffer sitting next to him.
"Was that inappropriate of me? Absolutely," he said. "Am I guilty? Yes."
On Tuesday, the Massa saga took another twist when The Washington Post, citing anonymous sources, reported that the House ethics panel has been investigating allegations Massa groped multiple male staffers in his office. Massa previously has claimed his misconduct was limited to using inappropriate language with staffers.
Appearing Tuesday on conservative commentator Glenn Beck's show on Fox News Channel, He later told CNN's Larry King, however, that "it is not true" that he groped a staffer.
Massa also took a different tack explaining why he left Congress.
"I wasn't forced out," he said. "I forced myself out."
Massa added that he did not live up to his own personal code of conduct.