Mutations and oncogenes--cause or effect

Widespread chromosomal abnormalities in high-grade ductal carcinoma in situ of the breast. Comparative genomic hybridization study of pure high-grade DCIS

For a variety of technical reasons it is rarely possible to study cytogenetic abnormalities in ductal carcinoma in situ (DCIS) using traditional techniques. However, by combining molecular biology and computerized image analysis it is possible to carry out cytogenetic analyses on formalin-fixed, paraffin-embedded tissue, using comparative genomic hybridization (CGH). The purpose of this study was to identify the prevalence of chromosomal amplifications and deletions in high-grade DCIS and to look specifically for unique or consistent abnormalities in this pre-invasive cancer. Twenty-three cases of asymptomatic, non-palpable, screen-detected, high-grade DCIS were examined using CGH on tumour cells obtained from histology slides. All cases showed chromosomal abnormalities. A wide variety of amplifications and deletions were spread across the genome. The most frequent changes were gains of chromosomes 17 (13 of 23), 16p (13 of 23), and 20q (9 of 23) and amplifications of 11q13 (22 of 23), 12q 24.1-24.2 (12 of 23), 6p21.3 (11 of 23), and 1q31-qter (6 of 23). The most frequent deletions were on 13q 21.3-q33 (7 of 23), 9p21 (4 of 23), and 6q16.1 (4 of 23). These findings indicate that high-grade DCIS is, from a cytogenetic viewpoint, an advanced lesion. There was no absolutely consistent finding in every case, but amplification of 11q13 was found in 22 of the 23 cases. The precise significance of this is unknown at present. This region of chromosome 11q harbours a number of known oncogenes, including cyclin D1 andINT2. It is likely that many of these findings are the result of accumulated chromosomal abnormalities, reflecting an unstable genome in established malignancy.

X-ray or gamma-ray leukemogenesis at Hiroshima and Nagasaki

Because of the uncertainty in dosimetry at the Japanese cities, I have recalculated the probability of x-ray or gamma-ray leukemogenesis using the revised doses given by the Livermore group. The theory is of the two hit type. The first hit damages DNA repair capability of base damage. The second hit causes derepression of a two repressor system. Inactivation of the first repressor permits synthesis of the second which will repress the expression of the leukocyte maturation gene. In comparing the observed data, I convert data expressed as mortality per year to leukemia incidence. I also supply evidence of the lack of the importance of chromosomal aberration and consider CML, AML, and ALL data lumped together. Agreement between theory and observation is good.

Differences between preneoplastic cells, neoplastic cells and their normal counterparts

A number of changes occur in preneoplastic and neoplastic cells as they progress towards a greater degree of malignancy. These alterations include genetic changes, epigenetic changes, surface alterations and alterations in intercellular interactions. In some instances, these changes are contributing factors to the degree of pathology noted, whilst other are resultant. In many situations, the relationship between these changes and the progression towards neoplasia is not understood. Nevertheless, it seems probable that these changes are ultimately involved in driving cells further along the path to neoplastic transformation. It is the purpose of this review to consider the changes which occur as cells progress from normality to being neoplastic, with particular reference to the cells of the oral mucosa, and the use to which detectable changes can be used as prognostic indicators.

Factors associated with the development of neoplasia

A number of factors have been associated with the development of the phenotypic expression of neoplastic disease. The following article reviews the evidence implicating these factors in carcinogenesis and considers them under the groupings of familial or genetic factors, dietary factors, hormonal factors, age and gender.

Activated N-ras controls the transformed phenotype of HT1080 human fibrosarcoma cells

To investigate whether the activated N-ras oncogene of HT1080 human fibrosarcoma cells contributes to the expression of the transformed phenotype, we have isolated flat revertants. In two independent revertant lines, an increase in chromosomal ploidy occurred without a concomitant increase in the number of copies of the N-ras transforming allele. Immunoprecipitation confirms that the level of the mutant N-ras p21 gene product in the revertants is correspondingly lower than in HT1080. Analysis of sporadic tumors derived from the revertant cells reveals an increased dosage of the transforming allele. The revertants also retransform after transfection of cloned activated ras oncogenes. These results imply direct participation of an N-ras oncogene in maintaining the transformed phenotype of a human tumor cell line.

Unstable visible mutations induced in Drosophila melanogaster by injections of oncogenic virus DNA into the polar plasm of early embryos

When RSV DNA cloned in pBR 322 or DNA of simian adenovirus Sa7 (C8) is injected into the pole plasm of embryos of various Drosophila stocks, the progeny of 1-70% of the surviving flies display visible mutations. The mutagenesis is partially directed: the loci mutating due to retrovirus and adenovirus DNA do not overlap. The majority of resulting mutants are characterised by high instability: reversions and new mutations occur in them, which sometimes spread over the whole population ("explosive" instability). The injected sequences are revealed by dot-hybridization in the DNA of many mutant strains, but only rarely by Southern blotting procedures. The results show that the microinjection of oncovirus DNA into embryos is an approach for obtaining highly unstable strains even from wild-type stable Drosophila stocks without crosses with MR lines or the introduction of P elements. The sets of unstable mutations induced by oncovirus DNA is different from those in hybrid dysgenesis.

Oncogenetics. A new emerging field of cancer

The belief that a neoplastic cell develops from a normal progenitor due to structural changes in DNA has been a fundamental basis of the study of the molecular biology of cancer. Recent technical advances in this field will give rise to conceptual advances and there is every reason to believe that a new field of cancer genetics is emerging, named here "Oncogenetics": a branch of genetics describing the cause of effects of genes causing neoplasia.

Mechanisms of multistep carcinogenesis: keys to developing in vitro approaches for assessing the carcinogenicity of chemicals

The process of neoplastic development is a complex combination of genetic and non-genetic changes within a tissue. It is, therefore, not surprising that a number of mechanisms exist by which chemicals influence this process. In designing short-term tests to detect potential carcinogens, the major emphasis to date has been on genetic assays. This is justified on both theoretical and practical grounds. Substantial evidence exists to support the hypothesis that genetic damage increases the probability of tumour development. Mutational assays for gene mutations, clastogenicity and aneuploidy induction are therefore extremely important tests for carcinogens. Unfortunately, few assays exist for detecting chemicals that induce gene amplification, and thus, if these are carcinogens that specifically induce this type of genetic change, they may go undetected. Because of a variety of possible differences between a chemical's activity in vivo and in vitro, it is to be expected that chemicals that are mutagenic in vitro may not have a significant carcinogenic effect in vivo. However, the potential harm of these chemicals to man does exist and may be expressed under different conditions (e.g. species- or organ-specific carcinogenic effects) or as non-carcinogenic hazards.

Molecular and cytologic analysis of DNA amplification in retinoblastoma

Amplification of two distinct genomic DNA segments is observed in homogeneously staining regions in two sets of retinoblastoma cell lines derived from two different patients. One DNA segment was known to have sequence homology to the c-myc oncogene, and both DNA segments had previously been shown to be amplified in neuroblastoma cells. The absolute degree of amplification differed in all cytogenetically distinct retinoblastoma cell lines tested. Also, the relative amplification of these two DNA segments was unequal within a given cell line. Minimal amplification of both DNA segments was also detected in DNA directly isolated from one primary retinoblastoma. Based on these and previous results, it is concluded that assembly of amplifiable, relocatable units in many human retinoblastoma and neuroblastoma cells may involve a complex process of differential recruitment of separate DNA segments that are located on human chromosome #2.