Beau Biden was first diagnosed with cancer in August 2013

The type of brain cancer that killed Beau Biden has not been disclosed. But assuming he suffered from a primary cancer — not one that spread from another part of the body — the most likely is a glioblastoma, an aggressive cancer of the brain's supportive tissue, two experts said. Patients with Grade 4 glioblastomas — the most aggressive type — survive a median of 14.6 months after diagnosis, said radiation oncologist Brian Alexander. Biden was first diagnosed in August 2013 and after surgery, radiation and chemotherapy returned to normal duties in November that year. But his cancer recurred this spring, and he began treatment again at Walter Reed National Military Medical Center.