Reduced expression of aphidicolin-induced common fragile sites in peripheral lymphocyte chromosomes of patients with B-cell chronic lymphocytic leukemia

Inversion of chromosome 12 and lineage promiscuity in hematologic malignancies

Rearrangements of the short arm of chromosome 12 are among the most common aberrations found in hematologic malignancies, including myelodysplastic syndromes, acute myelocytic leukemias, acute lymphoblastic leukemias, and non-Hodgkin lymphomas. We report on a group of 46 patients with a variety of myelocytic and lymphoid malignancies, all with an inversion of chromosome 12. Both pericentric and paracentric inversions occurred. The identified hotspots for breakage were p13 and q24. These correspond to gene-rich areas of known chromosome instability. The inv(12) is difficult to detect and may be misinterpreted as a partial deletion by routine cytogenetics. Fluorescence in situ hybridization studies revised the G-banding interpretations of a deleted 12p in some cases to an inversion. The inv(12) may occur as the sole abnormality in both myelocytic and lymphoid malignancies, suggesting lineage promiscuity as seen with MLL and ETV6 gene disruptions. The majority of patients with the inv(12) had complex karyotypic changes that predicted a poor prognosis. Of the 24 patients with known clinical follow-up, many were refractory to chemotherapy and overall survival was short.

Spontaneous breakage and fragile site expression in chronic lymphocytic leukemia

It has been suggested that genetic predisposition to cancer might be related to spontaneous chromosome instability or to fragile site expression. Therefore, spontaneous breakage and fragile sites were analyzed in nine untreated chronic lymphocytic leukemia (CLL) patients to determine their relation to cancer rearrangements. Five cases presented spontaneous gaps and breaks with a random distribution of breakpoints. In cultures treated with fluorodeoxyuridine or aphidicolin, 29 specific bands could be defined as fragile sites. A significant clustering of these sites was found with known common fragile sites (c-fra) and cancer breakpoints described in the literature. Most of these cancer breakpoints were involved in structural abnormalities associated with CLL (p < 0.00001). These data suggest that the expression of specific fragile sites might be related to structural chromosomal aberrations in CLL.

Expression of aphidicolin-induced fragile sites in lymphocytes of patients with breast cancer

The expression of fragile sites induced by aphidicolin (APC) was evaluated on metaphase chromosomes obtained from the peripheral blood lymphocytes of 26 women with breast cancer and 15 sex- and age-matched normal controls. Both the proportion of damaged cells (P < 0.001) and the mean number of gaps and breaks per cell (0.02 < P < 0.05) were significantly higher in the patient group. There were no differences in either the age-related fragile site levels or the expression of single fragile sites between patients and controls. Our findings indicate an increased genetic instability in women with breast carcinoma.