Fluorescence in situ hybridization panel for monitoring of minimal residual disease in patients with double minute chromosomes.

A double minute chromosome (dmin) is a small fragment of extrachromosomal DNA bearing amplified genes observed in malignancies. We investigated the incidence and characteristics of dmins in hematologic malignancies, and the quantitative changes during the treatment follow-up. Once a dmin was observed in conventional G-banding, it was characterized using fluorescence in situ hybridization (FISH) with the panel of MYC, NMYC, and MLL probes. Quantitative changes of malignant cells were measured using G-banding and FISH during the follow up. Dmins were observed in 1.23% of patients (6/489) at the initial diagnosis including 4 with MYC amplification, 1 with MLL and 1 with NMYC. All 6 had complex karyotypes and showed short overall survival (7.7 months). In follow-up specimens, FISH detected dmins in 11 cases out of which G-banding detected dmins in 9 cases. The number of dmins detected by FISH and G-banding did not correlate well. Amplification of NMYC in dmins is reported for the first time. A FISH panel composed of frequently amplified oncogenes (MYC, NMYC, and MLL) in dmins is useful for characterization of dmins. FISH is a sensitive method in detecting dmins and will be useful in monitoring of the minimal residual disease.