Senator Specter, 78, has had no symptoms of Hodgkin's disease aside from the PET scan findings, according to a statement released by his office.
Hodgkin's disease, also known as Hodgkin's lymphoma, is a cancer of the lymphatic system, which is part of your immune system.
In Hodgkin's disease, cells in the lymphatic system grow abnormally and may spread beyond the lymphatic system. As Hodgkin's disease progresses, it compromises your body's ability to fight infection.
According to Specter's office, his lymphoma is less advanced than his Hodgkin's disease when it was originally diagnosed in 2005.
In his recent book, "Never Give In: Battling Cancer in the Senate," Specter 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," Specter wrote. "Moreover, the event of death could never eclipse what is most important, which is how we spend the time we have."
Specter will now receive chemotherapy weekly over the next 12 weeks. During his previous diagnosis, he underwent six months of chemo.
Specter has long been an advocate of using federal dollars for cancer research and embryonic stem cell research. While bald from chemo in 2005, 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," Specter said at the time.
Specter, Pennsylvania's longest-serving senator, said he would continue his normal duties, and he still plans to run for re-election in 2010.
"Senator Specter has an excellent chance of again achieving a complete remission of his Hodgkin's disease," said Specter's oncologist, John H. Glick, M.D. of the Abramson Cancer Center of the University of Pennsylvania.
The early diagnosis of his recurrent Hodgkin's disease has a five-year survival rate of 60 percent, the doctor said.
Senator Specter had successful surgery for a brain tumor in 1993, which recurred in 1996 and was successfully treated. In 1998, in the middle of a re-election campaign, he underwent bypass surgery and post-operatively suffered cardiac arrest, from which he fully recovered.
"I've beaten some tough medical problems and tough political opponents and I expect to beat this too. I look forward to getting through this treatment and continuing to serve the people of Pennsylvania," Specter said.
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(Some information from The Associated Press.)
