Ring chromosomes in chronic myelogenous leukemia: an ominous finding

Ring chromosome in myeloid neoplasms is associated with complex karyotype and disease progression

Ring chromosome (RC) is a poorly understood genetic anomaly seen in myeloid neoplasms. This study aims to shed light on the clinical significance of this finding. We identified 96 cases of myeloid neoplasms with RC from 3 academic hospitals. Clinicopathologic features and overall (OS) and leukemia-free survival were reviewed and compared to cases of myeloid neoplasms lacking RC. We identified 59 acute myeloid leukemias (AML-RC) and 37 myelodysplastic syndromes (MDS-RC) with RC identified on routine karyotyping. Seventy-five percent of AML-RC and 97% of MDS-RC had complex (>3 independent cytogenetic abnormalities) karyotypes. The median OS of AML-RC with complex karyotype was significantly shorter than AML-RC patients with a non-complex (≤3 independent cytogenetic abnormalities) karyotype (P=.001), but similar to AML patients with complex karyotype lacking RC (P=not significant). Compared to complex-karyotype MDS lacking RC, MDS-RC patients had shorter leukemia-free survival (P=.016) and a trend for shorter OS (P=.10). RCs were sometimes lost after therapy or appeared during disease relapse, suggesting that they may be associated with genetic instability.

Constitutional chromosome aberrations as pathogenetic events in hematologic malignancies

A predisposition to tumor development is associated with some constitutional chromosomal abnormalities. Investigations of families with an apparent hereditary cancer and constitutional chromosome rearrangements have led to the molecular identification of tumor suppressor genes. Under the somatic mutation theory for the development of cancer, two mutational events are required. The first step may be a constitutional event and the second an acquired genetic mutation. Cytogenetic studies were performed on 5633 bone marrow specimens from patients with hematologic malignancies from a single institution. Fifty cases of constitutional chromosome aberrations were detected. Data collected from the literature and from our series are reviewed and compared with the incidence of specific constitutional chromosome aberrations in the newborn population. Possible mechanisms that may predispose individuals with constitutional chromosome aberrations to the development of a hematologic malignancy are reviewed.

Microdissection and FISH investigations in acute myeloid leukemia: a step forward to full identification of complex karyotypic changes

Complex chromosomal rearrangements in malignant hemopathies frequently remain unclarified because of paucity of material for further fluorescence in situ hybridization analyses and/or lack of suitable probes. Chromosome microdissection (MD) can be an adequate approach to elucidate chromosome aberrations unrecognizable by conventional karyotyping. We applied MD in two patients with acute myeloid leukemia (AML) and unidentified chromosome changes at karyotype. Microdissection of a ring chromosome in an AML-M5 case revealed 21q polysomy. In an AML-M4 case, MD of an add(15p) disclosed a t(8;15) with over-representation of both 8q22 and 8q24 bands. YAC probes were helpful in showing duplication of the ETO gene at 8q22, and amplification of C-MYC, at 8q24.

Loss of telomeric sequences in a ring derived from chromosome 8 in refractory anemia with excess of blasts in transformation

Using the fluorescence in situ hybridization technique, we analyzed a ring chromosome that appeared as a karyotype evolution in a patient affected by refractory anemia with excess of blasts in transformation. Metaphases hybridized with a chromosome-8-specific centromeric probe indicated that the ring retained the centromere of chromosome 8. Successively, utilizing a probe specific for all human telomeres, we observed that the ring lost telomeric sequences. This study demonstrated that the formation of a ring chromosome in hematologic disorders can cause loss of genetic material not revealed by banding techniques and therefore providing further proof of the advantages of molecular cytogenetic techniques.