Abstract: Viability of cancer cells (e.g., glioblastoma cells) can be reduced by administering mannose to the cancer cells; and applying an alternating electric field with a frequency between 100 and 500 kHz to the cancer cells. Susceptibility to treatment with an alternating electric field can be determined by measuring uptake of a PKM2 probe (e.g., [18F]DASA) before and after treatment with an alternating electric field. Notably, experiments show that the combination of mannose and the alternating electric field produces a synergistic anti-glioblastoma result.