Need a strong immune system to fight cancer

I am going through the old posts about cancer at Stephen' site, this is his take on cancer:

This raises the possibility that cancer is not simply the result of getting too old, but a very specific weakening of the immune system.

This is from empirical evidence obviously. But that evidence itself does not provide much hope here, the million dollar question is still that how to strenghten one specific individual's immune system. I need to read a lot more on immune system.