Sen. Arlen Specter, who beat Hodgkin's disease in 2005, yesterday revealed that the cancer has returned.

In a statement released by his office, Mr. Specter, 78, said the early recurrence of the cancer of the lymph system was revealed in a medical scan but that he has no symptoms.

The cancer was detected in lymph nodes in Mr. Specter's chest, the statement said, and a biopsy of one of the chest lymph nodes was positive for recurrence. A bone marrow biopsy was negative.

"I was surprised by the [Positron Emission Tomography] scan findings because I have been feeling so good," Mr. Specter said in the statement. "I consider this just another bump on the road to a successful recovery from Hodgkin's, from which I've been symptom-free for three years."

Mr. Specter, Pennsylvania's senior senator, said he has been advised that he will be able to continue to perform all the duties of his office, and the five-term Republican vowed that he will proceed in his pursuit of a sixth term in 2010, performing all the activities associated with a re-election campaign.

"I've beaten some tough medical problems and tough political opponents, and I expect to beat this, too," Mr. Specter said. "I look forward to getting through this treatment and continuing to serve the people of Pennsylvania."

Based on the location of the recurrence and the absence of symptoms, his lymphoma is considered Stage IIIA. This is much less advanced than his Hodgkin's disease when it was diagnosed in 2005, when it was Stage IVB. At that time, he was treated with six months of ABVD chemotherapy, and obtained a complete remission.

This time, he will undergo the Stanford V protocol of chemotherapy weekly over the next 12 weeks.

Mr. Specter has been making talk-show appearances recently touting his book, "Never Give In: Battling Cancer in the Senate," in which he credited hard work with getting him through the cancer treatments.

"An illness like Hodgkin's serves as a reminder that we have a limited time -- and how our time can end when we least expect it," he wrote. "Moreover, the event of death could never eclipse what is most important, which is how we spend the time we have."

Mr. Specter's oncologist, Dr. John H. Glick of the Abramson Cancer Center of the University of Pennsylvania, said the senator has "an excellent chance of again achieving a complete remission of his Hodgkin's disease," and credited the early detection of its recurrence with a five-year survival rate of 60 percent.

"He is in superb physical condition, with a normal physical examination and blood work, no symptoms of disease, plays squash regularly and follows a careful diet," Dr. Glick, an expert in Hodgkin's disease, said in the statement released by the senator.

During his 2005 treatment, Mr. Specter was bald from chemotherapy, yet he continued to fulfill his high-profile duty of chairman of the Senate Judiciary Committee as it confirmed John Roberts as chief justice of the U.S. Supreme Court. During the long hearings, he drank Gatorade and frequently wiped his face with tissue.

Mr. Specter has long been an advocate of using federal dollars for cancer research and embryonic stem cell research. While bald, he offered himself up at a Capitol Hill news conference as someone who could benefit from stem cell research.

"I've got a new hairdo, which you can all observe, and that is indicative of a problem which may well be helped by stem cell research if it were to go forward," he said at the time.

Representatives throughout government last night expressed surprise at Mr. Specter's announcement, yet universally voiced confidence that he again would persevere.

"As always, he and I have been working together on numerous matters affecting the people of Pennsylvania, and Arlen has demonstrated his usual energy and passion," said Sen. Bob Casey, the state's Democratic junior senator. " I have no doubt that Arlen will confront his health challenge with the same courage and determination that has marked his previous battles."

"Senator Specter exemplifies the toughness and hard work for which Pennsylvanians are famous," said U.S. Rep. Tim Murphy, R-Upper St. Clair. Mr. Specter had successful surgery for a brain tumor in 1993. It recurred three years later but was successfully treated. In 1998, he underwent bypass surgery and later suffered cardiac arrest.