TP53 and B-cell chronic lymphocytic leukemia: Interestingly, whereas TP53 mutations were found mainly as subclonal events that expanded over time favoring CLL progression and therapy resistance (33, 92, 116), NOTCH1 mutations were either clonal, representing early events in CLL development, or sublconal, indicative of an occurrence at late steps in CLL development and of a selection during disease progression (33, 112).