Can you tell me if cell phones cause brain cancer/tumors?

No: Somebody may tell you this is "still under study", but this pathologist thinks the idea is just wrong. No theoretical mechanism. You can find that anything causes anything if you do a bad study or ask the wrong questions, especially retrospectively. In one big study, the tumors were more common on the side opposite the cell phone. Stop worrying and enjoy the benefits of today's technology.

Dr Diede and another doctor agreed

Cell phone use: Cell phone radiation is low-frequency & low energy. It is actually nonionizing radiation. Unlike high frequency wave ionizing radiation, it is doubtful it can cause cancer in humans. Cell phone radiation was however, shown to ^ risk for developing schwannomas in rats & gliomas in other animal studies. REF: https://www.mskcc.org/blog/do-cell-phones-cause