The mankind needs about 200 years to close all factories and to use only green technologies, but even after that the Solar activity will be same or even higher. So, the problem of cancer will be always relevant.
Factories makes up the most of the business worldwide. I know some companies are applying environmental-friendly approach but still the most effective way to manufacture their products is using the factory equipment and chemicals. But in future, vaccines will be created to lessen the risk of cancer or completely cure it.