FISH patterns.

Representative FISH patterns of interphase and metaphase (2R) nuclei were obtained with the TEL (TRITC-labeled; red) andAML1 (FITC-labeled; green) probes in the 3 patients at diagnosis (D) and relapse (R). Most leukemic cells studied at diagnosis of all 3 patients (1D, 2D, and 3D) and at relapse for patient 3 (3R) had a TEL-AML colocalization (yellowish signal) and, as indicated by the missing red signal, a deletion of the secondTEL allele. A different pattern was observed in the relapse samples of patients 1 and 2 (1R and 2R). The signal for the secondTEL allele was clearly present. In addition, 2TEL-AML colocalizations indicated the duplication of the der21 that harbors the relevant gene fusion.