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Chronic myelomonocytic leukemia evolving from preexisting myelodysplasia shares many features with de novo disease.

The majority of chronic myelomonocytic leukemia (CMML) cases arise de novo; cases evolving from preexisting myelodysplasia (MDS) or myeloproliferative diseases have not been well-studied. We conducted the present study to determine the clinicopathologic features and to study possible underlying molecular and cytogenetic mechanisms involved in this evolution. Between April 1995 and November 2005, we identified 120 CMML cases, of which 20 (16.7%) had a previous diagnosis of MDS. Of the 20 patients with MDS, 6 had relative monocytosis at diagnosis. At the time of MDS to CMML evolution, mutations in JAK2 (V617F), FLT3 (ITD), K-ras-2, or N-ras were not acquired, and only 1 (6%) of 17 evaluable cases showed cytogenetic progression. The median time to evolution from MDS to CMML was 29 months, and the median survival following CMML development was 13 months. Three cases (17%) transformed to acute myeloid leukemia. These findings indicate that in some cases of otherwise typical MDS, the progenitor cells may have some capacity for monocytic proliferation at diagnosis and manifest rapid disease progression once a monocytic proliferation supervenes.