The Ras/MEK pathway plays critical roles in cancer cell death.21,23,24 Accordingly, the activated Ras pathway protects cells from ROS-induced cellular oxidation by increasing the expression of several antioxidant proteins.43 Interestingly, 5-ALA-PDT also activates the Ras/MEK pathway, which in turn reduces the induction of PCD in squamous carcinoma cells treated with 5-ALA-PDT.44 Therefore, MEK inhibition may reduce the expression of antioxidant proteins and promote cancer cell death induced by 5-ALA-PDT. This evidence concerns the gene MAP2K7 and squamous cell carcinoma.