75 years old man with cancer completes 100th marathon

In 2003, Don Wright, now 75, completed his first, and what he thought would be his last marathon. A few weeks after the race, he went to see his physician about what he thought was benign back pain. It turned out to be something much more serious.
His doctors diagnosed him with a rare blood cancer called multiple myeloma — and told him he had less than five years to live.
Multiple myeloma is a cancer formed by malignant plasma cells. According to the American Cancer Society, about 30,330 new cases of multiple myeloma will be diagnosed this year. The lifetime risk of getting multiple myeloma is about 0.7 percent.
"It is an incurable cancer," Wright told TODAY. "People are working on a cure and I would love to get the cure, but there isn't one yet."