The thing about cancer is, it's usually genetic degradation.
There are two things that need to occur for a cell to become cancerous
The first one is a malfunction of the system to detect harmful mutations - the cell is supposed to destroy itself
The second one is a malfunction of the system of determining when to copy itself - or more specifically when not to copy itself (if it is in the wrong location, or if there are already enough of the right type of cell in its location)
A cancerous cell makes copies of itself when it shouldn't, often in places it shouldn't be.
I think one interesting approach to combatting cancer is the use of a virus, such as the cold virus, to destroy cancerous cells - with the side effect of having a cold (wouldn't you rather have a cold for a few days than life threatening cancer?)
If a virus can be manufactured to target cancerous cells specifically, that may be quite effective.
One of the problems with cancer is that there are a lot of different types of it, often requiring a different type of treatment or cure.