Accordingly, while del(13q14.3) and to a much lesser extent, del(13q14) involving the RB1 gene and trisomy 12, were already detected in a small fraction of MBLlo clones, del(11q) and t(14q32) emerged at an MBLhi stage, whereas del(17p), del(11q23) and NOTCH1 mutations were only found in CLL. This evidence concerns the gene RB1 and B-cell chronic lymphocytic leukemia.