Myelodysplastic syndrome/acute myeloid leukemia supervening previously untreated chronic B-lymphocytic leukemia: demonstration of the concomitant presence of two different malignant clones by immunologic and molecular analysis.

The development of myelodysplastic syndrome (MDS) and/or acute myeloid leukemia (AML) has rarely been observed in patients with chronic B-lymphocytic leukemia (B-CLL). So far, the discussion concerning the pathogenesis of the simultaneous occurrence of these two malignancies has been speculative, opposing the theory of two separate malignant clones to the theory of a common stem cell malignancy. We describe the case of a 77-year-old woman who developed MDS after 8 years of an indolent course of B-CLL. The diagnosis of MDS was based on bone marrow (BM) morphology, showing the typical picture of a refractory anemia with excess of blasts (RAEB). The clinical course of MDS was aggressive, terminating in AML within only 6 months. Immunophenotyping of BM and peripheral blood (PB) cells revealed a CD34+/ CD13+/CD33-/CD19-blast cell population and a CD19+/CD5+ B-cell population with kappa light chain restriction. Molecular analysis of PB and BM demonstrated the presence of an immunoglobulin heavy chain (IgH) gene rearrangement by polymerase chain reaction (PCR) amplification of genomic DNA with three different pairs of consensus primers. Cell-sorting experiments showed that the IgH gene rearrangement was present only in the CD19+/CD34- B-cell population, but not in the CD34+/CD19- blast cells. Furthermore, X-chromosome inactivation pattern analysis revealed two differently methylated cell populations. These experiments demonstrate the concomitant existence of two different clones in a patient with CLL-MDS/AML.