While I cannot agree that "there is sufficient evidence that most cancers are based on some form of a microbe be it viral, fungal, bacteria etc", I readily agree that cannabis is wonderful for a number of cancers including brain cancers.
Most cancers are the result of a cellular defense mechanism which most often occurs as a result of prolonged oxidative stress - especially when the cellular terrain is less than healthy (such as under nourished and under hydrated). The trigger for the stress and resulting defense reaction is usually a toxin. Microbes can play a part, but they do not play the predominant part for the majority of cancers. Cancers can also be pleomprphic in nature and at various times have characteristics of viruses or bacteria or fungi - and cancers often reponsd to anti-bacterials, anti-virals and/or anti-funguls.
Theory aside, cannabis is a top item to use against cancer and would be one I would absolutely use in the instance of brain cancer.