Complex sentence: Although bone cancer (osteosarcoma) in the 1970s had a grim prognosis Grace chose to support Ian believing he could recover, even when a prognosis of a few weeks to live was given in late February--early March 1976.
Split into simpler sentences: Although bone cancer (osteosarcoma) in the 1970s had a grim prognosis Grace chose to support Ian believing he could recover. She supported Ian even when a prognosis of a few weeks to live was given in late February--early March 1976.