We found that the post-treatment decrease in the HIF-1α protein level better correlated with the cellular response than did the decreases in the total or phosphorylated EGFR and phosphorylated EGFR downstream substrate levels (ERK, Akt, and STAT3) in cancer cells with wild-type or tyrosine kinas domain-mutated EGFR. The gene discussed is HIF1A; the disease is cancer.