BCR and B-cell chronic lymphocytic leukemia: Recent studies have shown that unrelated CLL patients with near-identical BCR IGH profiles or identical receptor stereotypes are comparable to each other in terms of their clinical characteristics, genetic lesions, epigenetic changes, clinical course, and clinical outcome; for example, the largest stereotyped subset is subset #2 (IGHV3-21/IGLV3-21), which exhibits spliceosome genetic alterations, aggressive clinical course and poor outcome irrespective of SHM status.