For in vivo experiments, we chose selumetinib instead of U0126 as this MEK inhibitor is currently under phase II clinical trial for various cancers and is more suitable for animal studies.28,38 We first tested the 5-ALA-PDT sensitivity of mouse 4T1 mammary carcinoma cell line in vitro and found that MEK inhibition increased 5-ALA-PDT efficacy in 4T1 murine cells similar to the effect seen in human cancer cell lines (Supplementary Fig. S2). This evidence concerns the gene MAP2K7 and cancer.