Coexistent hairy cell leukaemia and chronic lymphocytic leukaemia.

Chronic lymphocytic leukaemia (CLL) and hairy cell leukaemia (HCL) are chronic B-cell lymphoproliferative disorders (B-LPDs) with distinct clinical, morphological and immunocytochemical features. Transformation of CLL into other B-LPDs (prolymphocytic leukaemia (PLL) and large cell lymphoma) is a well recognised phenomenon. One previous report has suggested that HCL may also arise by clonal evolution from CLL. We report the case of a 75 year old man in whom a diagnosis of coexisting HCL was made seventeen years after an initial diagnosis of CLL. Immunoglobulin heavy chain rearrangement studies suggest that the two B-LPDs developed independently. A steady increase in the bone marrow HCL component at the expense of the CLL component was observed with time, suggesting that HCL may have a growth advantage over CLL.