Biological and genetic cell heterogeneity is a landmark of most colorectal cancers and provides a frame for tumor progression as an evolutional process. Classical models have hypothesized that increased genetic instability may contribute to modulating and shaping malignant transformation. This is true for the small subset of colorectal cancers displaying microsatellite instability. For the rest of colorectal tumors, numerical and/or structural chromosomal alterations are the most prominent outcome of genetic disruption. These observations have prompted some investigators to hypothesize about the presence of chromosomal instability in these cells. To characterize chromosomal instability in cancer cells, we have analyzed genetic clonal divergence in three colorectal cancer cell lines considered to be archetypes in cancer research (HCT116, LoVo, and SW480). A dynamic setting was designed to allow the calculation of mutation rates. Comprehensive analyses at the chromosomal level revealed distinctive patterns of genetic divergence. Aneuploid SW480 cells displayed high rates of structural alterations (>100-fold) as compared with near diploid LoVo cells. Numerical alterations also occurred more frequently in SW480 cells but at low rates as compared with rearrangements in the chromosomically unstable SW480 cells. These results strengthen the role of structural instability in the generation of genetic heterogeneity in colorectal cancer.

This report describes the fourth case of heritable 18p monosomy, which was ascertained by prenatal diagnosis. Cytogenetic analysis of amniotic fluid cells by G-banding showed an apparently distal 18p chromosome deletion and a derivative X chromosome resulting from a translocation between the X and Y chromosomes. Analysis of peripheral blood lymphocytes from the parents by G-banding revealed the same chromosome 18 deletion in the mother, who did not have the X/Y translocation. Comparative genomic hybridization (CGH) studies confirmed the loss of chromosome region 18p11.3-pter previously detected, and eliminated the presence of unbalanced reorganizations of other chromosome regions. No subtle translocation was detected by fluorescence in situ hybridization (FISH) studies using whole chromosome specific painting probes. This is a new report of a heritable 18p monosomy. Although in our case the mother had several minor congenital malformations, the loss of 18p11.3 band was not associated with any obvious phenotypic alteration in the fetus.

Chromosomal imbalances were examined by comparative genomic hybridization in 30 cases of B-cell chronic lymphocytic leukemia (CLL) at diagnosis, in sequential samples from 17 of these patients, and in 6 large B-cell lymphomas transformed from CLL [Richter's syndrome (RS)] with no available previous sample. The most common imbalances in CLL at diagnosis were gains in chromosome 12 (30%), and losses in chromosomes 13 (17%), 17p (17%), 8p (7%), 11q (7%), and 14q (7%). The analysis of sequential samples showed an increased number of chromosomal imbalances in 6 of 10 (60%) patients with clinical progression and in 2 patients with stable stage C disease. No karyotypic evolution was observed in four cases with stable stage A disease and in one RS clonally unrelated to the previous CLL. Gains of 2pter, and 7pter, and losses of 8p, 11q, and 17p were recurrent alterations associated with karyotype progression. RS showed a higher number of gains, losses, total alterations, and losses of 8p and chromosome 9 than CLL at diagnosis. 17p losses were associated with p53 gene mutations and with a significantly higher number of chromosomal imbalances than tumors with normal chromosome 17 profile. However, no relationship was observed between 9p deletions and p16(INK4a) gene alterations. Losses of 17p and an increased number of losses at diagnosis were significantly associated with a shorter survival. These findings indicate that CLL has frequent chromosomal imbalances, which may increase during the progression of the disease and transformation into large cell lymphoma. Genetic alterations detected by comparative genomic hybridization may also be of prognostic significance.

We describe the presence of a high frequency of spontaneous chromosome aberrations in lymphocytes from six untreated patients with Hodgkin's disease. The characteristics of the chromosome abnormalities observed suggest the existence of a certain degree of chromosome instability in these cases, that could be a predisposing factor for the development of malignancies.

A complex familial chromosome translocation has been ascertained by combining classical cytogenetics and CISS (chromosomal in situ suppression). Cytogenetic analysis of a chorionic villus sample with G banding showed a 47,XX,-2, +der(2)t(2;22),+der(22)t(2;22) karyotype. Analysis of peripheral blood lymphocytes from the parents by G banding and CISS showed a more complex translocation in the father: 46,XY,-2,-11,-22, +der(2) t(2;11)(q13;q23), +der(11) t(11;22) (q23; qI1.2), +der(22) t(2;22) (ql3;ql1.2).Definitive analysis of cultured amniotic fluid cells showed a double partial trisomy of chromosomes 11 and 22. The couple decided to continue the pregnancy. The fetal karyotype was confirmed at birth. Clinical abnormalities present in our patient were typical of an unbalanced 11;22 translocation. Our findings confirm that chromosome painting techniques allow a better characterisation of complex chromosome rearrangements which may be difficult to detect in G banded karyotypes.

In a study of the expression of folate-sensitive fragile sites in five normal individuals using RPMI medium containing methotrexate (MTX), we observed a high frequency of "sister chromatid intercrossings" (SCI) that is, the intersection of sister chromatids. The location of SCIs corresponded to fragile sites in 54.2% of the cases. Of the SCIs observed in each individual, 43%-53% were located at the same bands as their expressed fragile sites. Furthermore when RPMI + MTX medium was used instead of F-10 medium, the incidence of SCIs increased tenfold. We suggest that SCIs could indicate the existence of a pre-lesion.

Sperm chromosome studies have shown that patients treated with chemotherapy for testicular cancer have a much higher incidence of chromosome abnormalities than patients treated for other types of cancer or than controls. In two out of four cases, penetration of zona-free hamster eggs was close to zero, indicating that after 2-7 years after treatment the functional capacity of the sperm had not been recuperated. The cytogenetic study of the spermatozoa shows that many of the abnormalities observed corresponded to structural aberrations that may not have a pathogenic effect in the production of abortions or of children with chromosome abnormalities.

Comparative genomic hybridization and fluorescence in situ hybridization were used to define genetic changes associated with multifocal bladder cancer and to investigate whether the genetic relationship between synchronous urothelial tumors is similar to that observed within different parts of the same tumor. We investigated 8 synchronous urothelial tumors from 3 patients and macroscopically different parts of the same tumor from 2 other patients. The most frequent imbalances were gains of 1q, 2p, and 17q, and losses in 4q. The high number of chromosome imbalances detected in the present report confirms that a high level of chromosome instability could be characteristic of multicentric bladder tumors. Comparative genomic hybridization profiles obtained from independent tumors belonging to the same patient allowed us to elaborate cytogenetic pedigrees portraying the accumulation of chromosome alterations as a form of clonal evolution from a single precursor cell. The analysis of different macroscopic parts of the same tumor allowed us to detect chromosomal heterogeneity and to delineate intratumor clonal evolution. Some chromosome regions that appeared as a gain in one subpopulation were amplified in others indicating a genetic evolution process. Identical processes were observed in different tumors of the same patient. Expansion of chromosome gains and losses between different parts of the same tumor as well as in different tumors of the same patient was also observed. Our results not only provide further evidence of a clonal relationship between different synchronous bladder tumors but also show that the intratumor heterogeneity present in different subpopulations of the same tumor reproduces the behavior of independent synchronous tumors in a same patient.