Double minute chromosomes and monosomy 7 in a lymphatic blast crisis of chronic myeloid leukemia

Cytogenetic patterns in 384 northern-Spanish patients with haematological disorders

During 1988-1991, we have conducted cytogenetic analysis in 384 consecutive patients with suspected neoplastic haematological diseases. A total of 404 samples were evaluated with banding techniques; 66 patients had myeloproliferative syndromes (MPS); 64, chronic myeloid leukaemia (CML); 50, acute nonlymphocytic leukaemia (ANLL); 40, myelodysplastic syndromes (MDS); 39, lymphoproliferative disorders (LPD); 37, acute lymphocytic leukaemia (ALL); 31 with non-Hodgkin lymphomas; and 57 patients had benign disorders. The frequencies and the type of detected chromosomal abnormalities were, in most diagnostic groups, within the limits of previous reports. For lymphomas, LPD, and MPS these frequencies were lower than expected. 144 cases (44.8%) of the 295 de novo diagnosed cases showed structural rearrangements. Breakpoints involved in structural rearrangements cluster to 35 bands of the standard 650-banded karyotype. We have observed eight cases with new chromosomal rearrangements.

Amplified c-MYC sequences localized by fluorescence in-situ hybridization on double minute chromosomes in acute myeloid leukemias

Double minute chromosomes (dmin) are small acentric fragments frequently observed when karyotyping human tumor cells. They are considered the cytogenetic manifestation of gene amplification. The finding of dmin in leukemia is a rare event usually associated with progression of the disease and unfavorable prognosis. We present four patients affected by myeloid disorders with an abnormal karyotype and a variable number of dmin. In an attempt to clarify the origin of the dmin and the amplified gene, we utilized a fluorescent in-situ hybridization (FISH) technique and a panel of specific probes. The results of the analysis indicate that, although chromosomes 8 are apparently uninvolved, dmin retained c-MYC sequencs in three cases. By observing previously reported cases, we found that the majority of patients with myeloid disorders and dmin showed an amplified c-MYC gene, regardless of the chromosomal abnormalities. The FISH technique proved to be informative in demonstrating gene amplification in both metaphase and interphase cells. Finally, in the one patient carrying a 20q deletion, FISH allowed the detection of a previously unreported translocation between a 16p and the 20q-, confirming the ability of the technique to understand complex karyotypes.

Localization of amplified MYC gene sequences to double minute chromosomes in acute myelogenous leukemia

Cytogenetic and molecular studies were performed on two dmin-bearing acute myelogenous leukemia (FAB-M2) samples. Both cases were characterized by complex karyotypes containing interstitial deletions of the long arm of chromosome 8 altering band 8q24.1, aberrations affecting the short arm of chromosome 17, and multiple double minute chromosomes (dmin). Using a 1.4 kb cDNA probe coding for the third exon of the MYC oncogene, DNA slot blots indicated MYC gene sequences were amplified in both samples. Fluorescence in situ hybridization using a 9.0 kb genomic probe for MYC was performed in one case and localized the amplified MYC gene sequences to the dmin. Neither patient achieved a complete remission using traditional induction chemotherapy. The complex karyology with amplification of MYC gene sequences appears to represent a poor prognostic subgroup of acute myelogenous leukemia.