Senator Arlen Specter’s cancer has returned. A statement released by his office said that a medical scan, followed by a biopsy, had detected an early recurrence of Hodgkin’s disease, which is a cancer of the lymph system. Mr. Specter, 78, a Republican from Pennsylvania, was treated for the same type of cancer in 2005 and was later given a clean bill of health. “I was surprised by the PET 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.”.