We previously demonstrated that, in resistant colon cancer, chronic lymphocytic leukemia, pleural malignant mesothelioma, non small cell lung cancer, and breast cancer, ERK1/2 phosphorylates and stabilizes the hypoxia-inducible factor-1α (HIF-1α), a strong inducer of Pgp [31,35,118,119,120]. This evidence concerns the gene MAPK3 and breast cancer.