AFF1 and acute lymphoblastic leukemia: While the t(4;11)(q21;q23) translocation that generates MLL–AF4 fusion protein can be used as a predictive marker of response, further work is needed to verify additional markers, such as deletion of IKZF1 or biallelic deletion of CDKN2A that were shown to sensitize pre-B-ALL to Btz and Cfz34.