I'm not a doctor, I am a scientist. Over thousands of years people have found various chemicals from plants to treat illness. In the last hundred pharmaceutical companies took the ones that worked and built an empire. If something is found to work then it is quickly picked up by a company and patented. If a pharma company is not interested then it likely doesn't do much. When we talk cancer/tumor growth, we are talking MAJOR interest from these companies. To put it into perspective, heroin is another recreational drug (and much more nefarious). It also has medical use. Thus pharmaceutical companies make billions on derivatives of heroin (Vicodin, Oxycontin, morphine, ect...).
Marijuana has been studied extensively for quite a while. It has a large recreational use and a very small pharmaceutical use. The reason its not used more medically is because for every possible use it has, there is a much more effective drug out there.
If you are looking for an excuse to use pot, that is your choice, no judgement. If you are wanting to control tumor growth....I am quite confident that it will not work.
Your neurosurgeon team will have all the latest advancements. Talk it over with them.