MAP2K7 and cancer: The subcellular localisation of the PS also contributes to the cellular sensitivity to PDT, as PDT-resistant cells have been shown to accumulate low amounts of PS in the mitochondria.48 Furthermore, some cancer cells develop resistance against PCD initiated by PDT-induced cellular oxidation.49,50 How these factors add to or interact with the Ras/MEK-dependent mechanisms and affect the cellular sensitivity to 5-ALA-PDT requires further investigation.