He was 82.
A longtime moderate Republican, Specter made headlines in 2009 when he announced that he was switching to the Democratic Party. He left office in 2011 after being defeated in the Democratic primary.
In 2005, Specter announced that he was being treated for non-Hodgkins Lymphoma. He recovered, but the illness resurfaced in 2008 and again in 2012. He was hospitalized in August.
The AP's full obituary is below.