Answer
The graph demonstrates that multiple mutations need to form for cancer to occur.
Work Step by Step
A single mutation is not enough to cause cancer, if that was possible the line would be horizontal and would be roughly the same age for all those affected. If there were only two mutations required the graph would slope up slightly, but it would require for the two cancerous cells to have been mutated in the same cell lineage. The age of the patient will correlate whether or not the initial mutation has already taken place. The graph demonstrates a tremendous spike after 50, and logically speaking a person will have many more than just 2 mutations by 50. While there is no specific number of mutations pinned down, it is clear that many are needed to cause cancer. A mutation will alter the the cells production in numbers, as well as the behavior from normal cells. This means that mutations cause more mutations and help the cancer to evolve.
