AFF1 and leukemia: To date, more than 100 such fusion partners have been described,22 but the most common ones represent about 80% of clinical cases (MLL fused with either ALL1-fused gene [AF] from chromosome 4 [AF4]/AFF1, eleven-nineteen-leukemia (ENL)/MLLT1, AF9/MLLT3, AF10/MLLT10 or eleven-nineteen lysine-rich leukemia (ELL)) and exist in related complexes involved in regulation of transcriptional elongation.23