When we investigated the cytotoxicity to PF-00477736 in the presence of dasatinib in the MCL cell line REC-1 with a primary resistance to Chk1 inhibitors [24], no reversion of drug resistance could be observed, suggesting that in this experimental system other molecular mechanisms are taking place (Supplementary Figure 6B). The gene discussed is CHEK1; the disease is mantle cell lymphoma.