Chronic lymphocytic leukaemia: one disease or two?

The discovery that the presence or absence of somatic mutations in immunoglobulin variable region genes separates chronic lymphocytic leukaemia (CLL) into benign and malignant subsets has raised the question as to whether CLL is one disease or two. Although there are similarities between morphology, immunophenotype and gene expression profiles between the two subsets, the very different natural histories and the immutability of one to the other suggests two diseases deriving from a common stem. It is proposed that a single intrinsic defect of B-lymphocytes dictates a particular reaction pattern -- partially activated, anergic and anti-apoptotic -- when the B-cell receptor is stimulated. The difference between the two subsets is determined by whether the receptor is stimulated conventionally within the germinal centre or unconventionally, outside it. The further differences, including CD38 expression and chromosomal abnormalities, are the consequences of further ongoing stimulation of the receptor leading to low-grade proliferation.