According to a family friend of former Pennsylvania Sen. Arlen Specter:

Early in the week of July 15th, the former senator collapsed while playing squash. He required emergency surgery to remove a growth in his abdomen that was affecting his breathing.

At that time, doctors discovered the reemergence of an aggressive cancer. He was severely ill with an infection following surgery and at one point that same week was not expected to survive even hours. 

Defying all medical expectations, since that time, he has responded remarkably well to vigorous chemotherapy and has been moved to a rehabilitation facility. He does go to the hospital for treatments, but is not currently in the hospital.

*** UPDATE *** Vicki Siegel Herson, a former Specter staffer says, “Anyone who knows Arlen Specter knows never to count him out as he will never ever give up."