Cellphones do have some effect on tumors because the Mobile phones use electromagnetic radiation in the microwave range. Other digital wireless systems, such as data communication networks, produce similar radiation.
This radiation can cause problems with the brain including tumers
The word tumor is derived from the Latin word for crab because cancers are often very irregularly shaped, and because, like a crab they attach and it takes a lot of force to make them let go.
There is no known cure for tumors but there are treatments to tumors such as chemotherapy or simply having them remove it which could be potentially dangerous. Which can cause brain damage or in extreme cases death.
Tumors aren't the only threats from cellphone radiation there is also radiation cancer which is just as deadly but requires you to spend more time in the hospital.