BCR and B-cell chronic lymphocytic leukemia: The degree of mutation of the genes encoding the immunoglobulin heavy chain clonotype of the BCR is among the most robust prognostic tools for CLL/SLL, dividing patients with ‘unmutated’ CLL (U-CLL) as having more aggressive disease outcomes, or so-called ‘mutated’ CLL (M-CLL) as having more indolent disease course [17].