NOTCH1 and B-cell chronic lymphocytic leukemia: In chronic lymphocytic leukaemia (CLL), recurrent NOTCH1 mutations were observed at all disease stages, whereas mutations in the paralogs NOTCH2, NOTCH3 and NOTCH4 were rare events with frequencies <1% (NOTCH2 in 0.9%; NOTCH3 in 0.7%; NOTCH4 in 0.6%) (4).