Problems with interphase fluorescence in situ hybridization in detecting BCR/ABL-positive cells in some patients using a novel technique with extra signals

Interphase fluorescence in situ hybridization (I-FISH) is frequently used to monitor the response to therapy in various hematological malignancies. We performed a comparison of I-FISH, metaphase FISH (C-FISH). conventional cytogenetics, spectral karyotyping (SKY) and PCR for the: detection of the t(9,22) and the BCR:ABL rearrangement in 32 patients with chronic myelogenous leukemia (CML). FISH was done using a novel commercial probe set (VYSIS LSI BCR! ABL ES). which is designed to reduce the rate of false-positive results by marking the argininosuccinate synthetase (ASS) gene and thus providing an extra signal on chromosome 9. Our data indicate, that a substantial number of BCR:ABL-positive patients (n=5 patients, 3 with Ph. 2 with masked Ph) present negative results using this probe set in I-FISH analyses, because they did not fulfill the scoring criteria. In fact, the ASS region, which usually remains on 9q in Ph CML. appears to be lost or translocated. Due to these results we recommend that the initial diagnosis as well as the: follow-up of patients with Ph+ leukemias should not be based on a single technique but should integrate results of cytogenetics and molecular biology. (C) 2001 Elsevier Science Inc.. All rights reserved.