Furthermore, the CD5low and CD5high sequences do not subcluster significantly into distinct groups on the phylogenetic tree (p = 0.509; Supplementary Fig. E6, online only, available from www.exphem.org), suggesting that there is no parsimonious route to a single or low number of switch events followed by fixed BCR sequence lineages in CD5high and CD5low CLL. This evidence concerns the gene BCR and B-cell chronic lymphocytic leukemia.