Several Apollo astronauts both moon walkers and CMPs have passed away. Though only 2 have died from cancer.
John (Jack) Swigert passed awy in 1982
Alan Shepard died in 1998 from leukemia.

Most of the deceased apollo 7-17 astronauts have died from heart attacks.
Deke Slayton died in 1993 from a brain tumour despite not having flown through the van allen belts. Its difficult to attribute any of these deaths to space flight related hazards,including radiation for 2 reasons:
1. Some there seems no link between where an astronaut flew and their subsequent health problems.
2.Most of these men lived into their 70s by which time they may have had such health problems regardless of their careers.