Aside from helping with the pain and nausea, cannabis is extremely useful in the fight against primarily brain tumor, and all cancer really. It forces the cancer to kill itself and then eat itself.
Sources:
Cannabinoid action induces autophagy-mediated cell death through stimulation of ER stress in human glioma cells
http://1.usa.gov/ZIKz06
Delta9-tetrahydrocannabinol (THC) induces apoptosis in C6 glioma cells
http://1.usa.gov/128uuiF
A combined preclinical therapy of cannabinoids and temozolomide against glioma
http://1.usa.gov/ZIKGsP