BCR and B-cell chronic lymphocytic leukemia: Considering the IGHV gene usage and relating it with the distribution of IGHV gene in stereotyped BCR clusters, it has been observed that cases expressing the IGHV3-23 gene are constantly absent from stereotyped BCR clusters [106], despite that IGHV3-23 is the second most frequently used and usually M IGHV gene in CLL [89,90,92].