Both BETIs and Chk1 inhibitors have previously been shown to have efficacy in cultured melanoma cells and Chk1 has even been suggested to be essential for the melanocytic lineage.26 We have demonstrated that Myc-induced lymphoma cells undergoing replication stress, because of ATR inhibition, are sensitive to BETIs.19 Here we wish to investigate whether or not this finding can be extended to solid cancers. This evidence concerns the gene CHEK1 and melanoma.