“I am going to be fine in all this,” said Mr. Dodd, who spoke from his office in Hartford with his wife, Jackie Clegg Dodd, alongside him. “This is very common. If you’ve got to have cancer, I am told by some doctors, it’s the slowest growing, the best one to have, the most manageable.”

Image Christopher Dodd and his wife Jackie Clegg Dodd spoke at a news conference in Hartford, Conn., on Friday. Credit... Jessica Hill/Associated Press

His announcement came as a surprise to people in politics and elicited sympathy from many, including his likely Republican rival in the 2010 Senate race, former Representative Rob Simmons. It also set off questions about how the cancer would affect his political future.

At his news conference, Mr. Dodd moved to dispel any notion that he might not seek another term. “I’m running for re-election,” he said without prompting. “Now, I’ll be a little leaner and a little meaner. But I am running.”

Then he added with a laugh: “I’ll be running without a prostate. That will make a better candidate, I think.”

Mr. Dodd is the chairman of the Senate banking committee, but he is currently at the center of the government’s battle over health care, acting as chairman of the Senate Health, Education, Labor and Pensions Committee for his close friend Senator Edward M. Kennedy, the Massachusetts Democrat, who is fighting brain cancer.