Detection of translocation 8;21 on interphase cells from acute myelocytic leukemia by fluorescence in situ hybridization and its clinical application.

To detect a translocation (8;21)(q22;q22) in interphase cells by fluorescence in situ hybridization (FISH), we investigated three probe combinations: single-color hybridization with two cosmid probes (cY8 and cY3), single-color hybridization with four cosmid probes (cY8, cY3, cY107, and cYR4), and dual-color hybridization with two cosmid probes (cY107 and cYR4) from the AML1 gene flanking or overlapping the breakpoint region. Over 95% of nuclei gave sufficient signals in all three probe combinations, and the detection rates were not statistically different among them. Among 18 patients examined at diagnosis, 12 with t(8;21) were also monitored for the number of residual leukemic cells after chemotherapy or bone marrow transplantation (BMT). There were some discrepancies between morphology and genetic (especially FISH) results at partial, or even complete remission. As leukemic cells with t(8;21) can maturate, morphological assessment alone is insufficient to evaluate the residual leukemic cells. Interphase FISH provided more precise information about the clinical status of patients with an 8;21 translocation after treatment.