Regarding each specific cytogenetic/molecular alteration, a tendency towards a greater frequency of del(13q) and trisomy 12 was observed from MBLlo to MBLhi and CLL clones, although differences only reached statistical significance for the frequency of del(13q14) involving the RB1 gene (P = 0.04). The gene discussed is RB1; the disease is B-cell chronic lymphocytic leukemia.