Methods of treating tumors by administering compounds to a patient are provided. Compounds such as pro drugs, e.g., 5-aminolevulinic acid (5-ALA), may be administered to the patient orally, by injection, intravenously, or topically, which then accumulate preferentially as compounds such as protoporphyrin IX (PpIX) in tumor cells. After such accumulation, compounds such as PpIX are then activated in various aspects to treat tumors cells, thereby treating cancer. Cancers such as glioblastoma may be treated.