MICROSATELLITE INSTABILITY IS RARE IN THE CLINICAL COURSE OF MYELODYSPLASTIC SYNDROME STUDIED WITH DNA FROM FRESH AND PARAFFIN-EMBEDDED TISSUES

Microsatellite instability (MSI) has been reported to occur in various types of malignant neoplasms. We performed a polymerase-chain-reactio n-based assay for MSI between the initial and the most recently availa ble (''latest'') samples from 23 patients with myelodysplastic syndrom e (MDS). Of these patients, 15 were informative at more than three mic rosatellite loci. Seven patients showed as increase in leukemic cells while 8 patients did not during the interval between the two analyses. Only 1 of the patients, who had refractory anemia with excess;blasts, which changed to acute myelogenous leukemia, showed microsatellite al teration at the analysis times. Among all 23 patients, two alterations were detected in the 42 informative paired samples that showed an inc rease in leukemic cells (4.8%), while none was directed in the 59 pair ed samples without such an increase. In total, therefore only two alte rations were detected among 101 informative paired samples (2%). This indicates that MSI is rare in the clinical course of MDS irrespective of disease status, and is consequently not a critical genetic event fo r disease progression in most MDS patients.