Aneuploidy is a well recognised feature of human tumours, but the investigation of its biological and clinical significance has been hampered by technological constraints. Quantitative DNA analysis reflects the total chromosomal content of tumour cells and can now be determined rapidly and reliably using flow cytometry; this has resulted in renewed interest in its potential clinical applications. This article reviews the accumulating evidence that tumour ploidy reflects the biological behaviour of a large number of tumour types and that diploid tumours in particular have a relatively good prognosis. The measurement of tumour ploidy is likely to become a valuable adjunct to the clinical and histopathological assessment of cancers.

https://jcp.bmj.com/content/jclinpath/37/9/961.full.pdf

Clinical and biological significance of aneuploidy in human tumours.

The many complex phenotypes of cancer have all been attributed to “somatic mutation.” These phenotypes include anaplasia, autonomous growth, metastasis, abnormal cell morphology, DNA indices ranging from 0.5 to over 2, clonal origin but unstable and non-clonal karyotypes and phenotypes, abnormal centrosome numbers, immortality in vitro and in transplantation, spontaneous progression of malignancy, as well as the exceedingly slow kinetics from carcinogen to carcinogenesis of many months to decades. However, it has yet to be determined whether this mutation is aneuploidy, an abnormal number of chromosomes, or gene mutation. A century ago, Boveri proposed cancer is caused by aneuploidy, because it correlates with cancer and because it generates “pathological” phenotypes in sea urchins. But half a century later, when cancers were found to be non-clonal for aneuploidy, but clonal for somatic gene mutations, this hypothesis was abandoned. As a result aneuploidy is now generally viewed as a consequence, and mutated genes as a cause of cancer although, (1) many carcinogens do not mutate genes, (2) there is no functional proof that mutant genes cause cancer, and (3) mutation is fast but carcinogenesis is exceedingly slow. Intrigued by the enormous mutagenic potential of aneuploidy, we undertook biochemical and biological analyses of aneuploidy and gene mutation, which show that aneuploidy is probably the only mutation that can explain all aspects of carcinogenesis. On this basis we can now offer a coherent two-stage mechanism of carcinogenesis. In stage one, carcinogens cause aneuploidy, either by fragmenting chromosomes or by damaging the spindle apparatus. In stage two, ever new and eventually tumorigenic karyotypes evolve autocatalytically because aneuploidy destabilizes the karyotype, ie. causes genetic instability. Thus, cancer cells derive their unique and complex phenotypes from random chromosome number mutation, a process that is similar to regrouping assembly lines of a car factory and is analogous to speciation. The slow kinetics of carcinogenesis reflects the low probability of generating by random chromosome reassortments a karyotype that surpasses the viability of a normal cell, similar again to natural speciation. There is correlative and functional proof of principle: (1) solid cancers are aneuploid; (2) genotoxic and non-genotoxic carcinogens cause aneuploidy; (3) the biochemical phenotypes of cells are severely altered by aneuploidy affecting the dosage of thousands of genes, but are virtually un-altered by mutations of known hypothetical oncogenes and tumor suppressor genes; (4) aneuploidy immortalizes cells; (5) non-cancerous aneuploidy generates abnormal phenotypes in all species tested, e.g., Down syndrome; (6) the degrees of aneuploidies are proportional to the degrees of abnormalities in non-cancerous and cancerous cells; (7) polyploidy also varies biological phenotypes; (8) variation of the numbers of chromosomes is the basis of speciation. Thus, aneuploidy falls within the definition of speciation, and cancer is a species of its own. The aneuploidy hypothesis offers new prospects of cancer prevention and therapy. Cell Motil. Cytoskeleton 47:81–107, 2000. © 2000 Wiley-Liss, Inc.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/1097-0169%28200010%2947%3A2%3C81%3A%3AAID-CM1%3E3.0.CO%3B2-%23

Aneuploidy, the somatic mutation that makes cancer a species of its own.

In eucaryotic cells, incompletely replicated or damaged chromosomes induce cell cycle arrest in G2 before mitosis, and in the yeast Saccharomyces cerevisiae the RAD9 gene is essential for the cell cycle arrest (T.A. Weinert and L. H. Hartwell, Science 241:317-322, 1988). In this report, we extend the analysis of RAD9-dependent cell cycle control. We found that both induction of RAD9-dependent arrest in G2 and recovery from arrest could occur in the presence of the protein synthesis inhibitor cycloheximide, showing that the mechanism of RAD9-dependent control involves a posttranslational mechanism(s). We have isolated and determined the DNA sequence of the RAD9 gene, confirming the DNA sequence reported previously (R. H. Schiestl, P. Reynolds, S. Prakash, and L. Prakash, Mol. Cell. Biol. 9:1882-1886, 1989). The predicted protein sequence for the Rad9 protein bears no similarity to sequences of known proteins. We also found that synthesis of the RAD9 transcript in the cell cycle was constitutive and not induced by X-irradiation. We constructed yeast cells containing a complete deletion of the RAD9 gene; the rad9 null mutants were viable, sensitive to X- and UV irradiation, and defective for cell cycle arrest after DNA damage. Although Rad+ and rad9 delta cells had similar growth rates and cell cycle kinetics in unirradiated cells, the spontaneous rate of chromosome loss (in unirradiated cells) was elevated 7- to 21-fold in rad9 delta cells. These studies show that in the presence of induced or endogenous DNA damage, RAD9 is a negative regulator that inhibits progression from G2 in order to preserve cell viability and to maintain the fidelity of chromosome transmission.

Characterization of RAD9 of Saccharomyces cerevisiae and evidence that its function acts posttranslationally in cell cycle arrest after DNA damage.

Purpose: It has been shown previously that sensitivity to the induction of chromosome damage by ionizing radiation is, on average, higher in G2 or G0 lymphocytes of breast cancer patients than of normal healthy controls. The authors suggested that elevated chromosomal radiosensitivity may be a marker for breast cancer predisposition. To investigate whether the G0 micronucleus assay is a true surrogate for the more demanding G2 metaphase assay, both tests have now been performed on the same blood samples from 80 patients. Methods: For the G0 micronucleus assay, cells were exposed to 3.5Gy 137Cs gamma -rays 6 h before mitogenic stimulation, treated with cytochalasin B at 24 h post-stimulation and harvested at 90 h. For the G2 assay, at 72 h after stimulation cells were given 0.5Gy X-rays and harvested 90 min later. Results: Previous observations were confirmed, now with much larger numbers of donors, in that approximately 40% of breast cancer patients showed elevated sensitivity in the G2 assay (135 patient...

Increased chromosomal radiosensitivity in breast cancer patients: a comparison of two assays

Association of biallelic BRCA2/FANCD1 mutations with spontaneous chromosomal instability and solid tumors of childhood.

The amount of chromosome damage in peripheral blood lymphocytes following 400 rads G0 X-irradiation in 10 of 11 hereditary retinoblastoma patients was shown to be intermediate between that in normals and damage in trisomy 21 patients. The difference between normals and hereditary retinoblastoma patients was small, it varied between hereditary retinoblastoma patients, and no difference was detected following 200 rads G0 X-irradiation. No difference was found in levels of spontaneous chromosome damage in hereditary retinoblastoma patients, trisomy 21 patients, and normals. These results suggest that, although sensitivity to ionizing radiation may be associated with hereditary retinoblastoma, the observed difference is so small that it is probably not the major effect of the gene predisposing to retinoblastoma.

http://cancerres.aacrjournals.org/content/canres/41/9_Part_1/3635.full.pdf

Chromosome damage in G0 X-irradiated lymphocytes from patients with hereditary retinoblastoma.

Publisher Summary This chapter focuses on dominants susceptibility to cancer in man. The survey of dominantly inherited cancer susceptibility and the consideration of the general nature of dominant inheritance allows a number of tentative conclusions to be reached. (1) There is no reason to suppose that, in terms of the genetic lesion at the DNA or chromosome level, dominant genes for cancer susceptibility prove to be any different from other dominant or recessive genes and they may be base changes, frame shifts, deletions, inversions, and duplications. (2) Implicit in the nature of dominance and so unlike recessive genes, the expression of the gene is critically dependent on the response of the normal allele to the presence of a gene with abnormal function and also to somatic damage to, or the malfunction of, the normal allele. (3) There is little evidence that the members of this group of genes are expressed in an overt way during embryogenesis. (4) Several hypotheses have been put forward to explain the action of these genes in producing focal, tissue-specific cancer susceptibility.

Dominant Susceptibility to Cancer in Man

While it would be satisfying to find that the same cellular process, or even a group of closely related processes, leads to the development of neoplasia, there is no necessity to believe that such a common pathway exists, since cancer includes many diverse diseases, the etiology, biology, clinical presentation, therapy, and prognosis of which will differ very greatly. Our knowledge of cancer cells depends largely on the behavior of the cells in culture and the measurement of various parameters that are not necessarily linked in any causal way with the neoplastic state. From these studies, however, have arisen a number of theories on the nature of neoplasia. For example, it is quite clear that the cell surface of cancer cells is abnormal in many different ways.304 There are new antigenic determinants; there may be altered glycoprotein and sialoprotein structures on the cell surface; the electrical charge and therefore the electrophoretic mobility of the cells may be altered; the absence of some material from the cell surface may also be associated with the acquisition of neoplastic properties (e.g., LETS protein29). Cancer cells also have altered contact relationships with other cells in culture in that they will fail to respond to the presence of other cells and move over or under them, whereas normal cells will usually stop or change direction on coming into contact with other cells.

Chromosomes and neoplasia.

At an open meeting of cytogeneticists held during the 6th International Congress of Human Genetics in Jerusalem, a new Standing Committee for Human Cytogenetic Nomenclature was elected to serve for a period of five years. The members are Martin Bobrow (Europe), Maimon Cohen (USA and Canada), Uta Francke (USA and Canada), David Harnden (Europe), Patricia Jacobs (USA and Canada), Grant Sutherland (Asia and Australasia), and Jacob Wahrman (Middle East and Africa). The committee would like to receive comments on ISCN (1978) and ISCN (1981) to help with future revisions.

David G. Harnden

Papers

Chromosome damage in G0 X-irradiated lymphocytes from patients with hereditary retinoblastoma.

Dominant Susceptibility to Cancer in Man

Chromosomes and neoplasia.

Human Cytogenetic Nomenclature

Human Cytogenetic Nomenclature