RETROSPECTIVE ANALYSIS OF CLONALITY AND DETECTION OF RESIDUAL DISEASEIN MYELOID-LEUKEMIA BY FISH ON LONG-TERM STORED BONE-MARROW SMEARS

Background: Fluorescence in situ hybridization (FISH) has allowed the detection of numerical chromosomal aberrations in interphase nuclei on fresh or frozen smears of leukemia. Methods: To analyze clonality and residual disease in myeloid leukemia retrospectively we applied FISH to bone marrow smears stored at ambient temperature for up to 9 years. Results: When hybridization efficiency was investigated on stored con trol smears from patients without hematological malignancy, more than 96% of nuclei showed the expected number of signals using DNA probes s pecific for chromosome 7, X or Y. In combination with cell morphology, we observed much higher hybridization efficiency in blasts and granul omonocytic cells compared with lymphoid and erythroid cells. On the ba sis of good hybridization efficiency for old smear specimens, we appli ed FISH to stored bone marrow smears of myeloid leukemias, in which ei ther loss of chromosome 7 or loss of sex chromosomes had been verified previously by conventional cytogenetics (one patient with chronic mye lomonocytic leukemia (CMML) and four with acute myeloid leukemia (AML; three M2 and one M7)). As a result, the loss of chromosome was detect ed in blasts from all patients and was observed in mature granulocytes , except in M7. In the CMML patient and one AML (M2) patient with t(8; 21), lymphoid and erythroid cells also showed the loss of chromosomes, suggesting that it should occur at stem-cell level. A high amount of residual disease was detected in the morphological remission samples i n one AML (M2) patient after induction therapy. The patient eventually succumbed to relapse. Conclusion: Thus, the present FISH technique is useful to analyze the clinical significance of clonality and the resi dual disease in myeloid leukemia, retrospectively.