Allele losses and onco-suppressor genes

Carcinogenesis: basic principles

Many steps are required to convert a normal cell into a cancerous one. The cancer cell must be able to multiply under conditions that a normal cell would not and to invade surrounding tissue and spread throughout the body. Both genetic changes, such as activation of oncogenes or inactivation of tumor suppressor genes, and epigenetic changes, such as stimulation of cell proliferation, contribute to the development of cancers. Chemical agents can increase the probability of malignant transformation by inducing mutations that can ultimately lead to tumor formation, by promoting the development of tumors in cells with preexisting genetic damage, or by increasing the rate of acquisition of malignant traits by benign tumors. Chemical carcinogens are structurally diverse, but all initiating agents are either already electrophiles or can be converted to electrophilic reactants through metabolic activation. Genetic and environmental factors can alter an individual's ability to metabolize carcinogens, to repair DNA damage, and to respond to mitogenic stimuli, all of which can alter susceptibility to chemical carcinogenesis. The incidence and time required for appearance of tumors appear to be dose-related, but the existence of no-effect doses of carcinogens remains controversial.

The polymerase chain reaction in histopathology

Thanks to the advent of the polymerase chain reaction (PCR) molecular genetic study of histological samples is now a relatively straightforward task and the vast histopathology archives are now open to molecular analysis. In this review we outline technical aspects of PCR analysis of histological material and evaluate its application to the diagnosis and study of genetic, infectious and neoplastic disease. In addition, we describe a number of newly developed methods for the correlation of PCR analysis with histology, which will aid the understanding of the molecular basis of pathological processes.

Paraffin wax-embedded material as a source of DNA for the detection of somatic genetic changes

Loss of genetic material, corresponding to chromosomal deletions, has been detected in a wide range of tumours and may indicate the position of a tumour suppressor gene. In order to identify the position of such a gene more precisely, many tumour samples must be studied until a minimum consensus deletion is characterized. This process is particularly necessary for lung tumours in which the deletion in chromosome 3, seen with such high frequencies in all histological subtypes, is almost always large. We have recently described the use of the polymerase chain reaction (PCR) for restriction fragment length polymorphism (RFLP) analysis of DNA isolated from small bronchial biopsies of lung tumours. In this study we adapted this technique to allow genotyping of DNA isolated from paraffin wax-embedded material (PWEM) microdissected from glass slides. We have investigated 12 lung tumours at polymorphic loci on chromosome 3 and showed allelic loss in all samples. In adapting PCR-RFLP analysis for DNA isolated from PWEM, we have concentrated on those approaches which might be adaptable to routine clinical practice. Somatic genetic changes are now being identified in many tumour types, and this information is expected to be of diagnostic and prognostic significance.