Parallel routes of human carcinoma development: implications of the age-specific incidence data

How Research on Human Progeroid and Antigeroid Syndromes Can Contribute to the Longevity Dividend Initiative

Although translational applications derived from research on basic mechanisms of aging are likely to enhance health spans and life spans for most of us (the longevity dividend), there will remain subsets of individuals with special vulnerabilities. Medical genetics is a discipline that describes such "private" patterns of aging and can reveal underlying mechanisms, many of which support genomic instability as a major mechanism of aging. We review examples of three classes of informative disorders: "segmental progeroid syndromes" (those that appear to accelerate multiple features of aging), "unimodal progeroid syndromes" (those that impact on a single disorder of aging), and "unimodal antigeroid syndromes," variants that provide enhanced protection against specific disorders of aging; we urge our colleagues to expand our meager research efforts on the latter, including ancillary somatic cell genetic approaches.

Facts and fiction: premalignant lesions of lung tissues

Lung cancer is now the leading cause of death from cancer in Australia. Most patients are diagnosed with late-stage disease. Although diagnosis at pre-invasive stages could theoretically improve outcomes, mooted precursor lesions are often asymptomatic and often undetectable by non-invasive investigations. Nonetheless, they merit study to identify early and essential molecular steps involved in lung carcinoma pathogenesis, with the aim of developing therapies targeted against one or more such steps. Some lung cancers appear to develop via a series of progressive morphological changes with correlating molecular alterations, but others seem to arise in histologically normal epithelium, and these differences may reflect anatomically and functionally distinct epithelial compartments of the respiratory tract. Pre-invasive precursor lesions recognised by the World Health Organization (WHO) include squamous metaplasia with dysplasia and carcinoma in situ, atypical adenomatous hyperplasia, and diffuse idiopathic pulmonary neuroendocrine cell hyperplasia. Other lesions that likely represent pre-invasive lesions, but which are not currently WHO-listed, include human papillomavirus (HPV)-related respiratory papillomatosis and mesothelioma in situ. No single cancer stem cell marker has been identified. Field cancerisation plays an important role in lung cancer development, and includes the spread of pre-invasive clones along the respiratory epithelium or the occurrence of multiple separate foci of pre-invasive abnormalities such as squamous dysplasia and carcinoma in situ.In addition to well-characterised step-wise progression in squamous cell carcinomas and some adenocarcinomas, alternative pathways exist, and are currently being investigated. In addition, molecular techniques, including miRNA screening on blood samples or cytology samples--such as sputum samples--may become clinically relevant and more accurate in predicting lung cancer progression.

Age-specific incidence data indicate four mutations are required for human testicular cancers

Normal human cells require a series of genetic alterations to undergo malignant transformation. Direct sequencing of human tumors has identified hundreds of mutations in tumors, but many of these are thought to be unnecessary and a result of, rather than a cause of, the tumor. The exact number of mutations to transform a normal human cell into a tumor cell is unknown. Here I show that male gonadal germ cell tumors, the most common form of testicular cancers, occur after four mutations. I infer this by constructing a mathematical model based upon the multi-hit hypothesis and comparing it to the age-specific incidence data. This result is consistent with the multi-hit hypothesis, and implies that these cancers are genetically or epigenetically predetermined at birth or an early age.

An exposure driven functional model of carcinogenesis

The understanding of general models of carcinogenesis have not advanced substantially over the last years despite a rapidly increasing amount of detailed knowledge in molecular biology, genetics and epidemiology, and it has been difficult to come up with specific hypotheses in order to test existing models. Current multistage models consider mutations per se as the driving forces of carcinogenesis. In contrast, novel knowledge in epidemiology and basic research combined with upcoming large scale technologies of transcriptomics and epigenetics offers a new model--the exposure driven functional model. In this model exposures to carcinogenic substances are the determinants of the carcinogenesis leading to functional changes in gene regulation and to mutations. The diversity of exposures and functional changes could give not one, but many different cancer phenotypes. Under this novel model, cessation of exposure could arrest or reverse the carcinogenic process. To test hypotheses based on this novel model, studies with valid exposures measurements, biological material suitable for all "-omics" analyses, and a design that takes into account the time order principle of causality are a prerequisite. In epidemiology, such designs have been proposed, while in basic genetic research most designs only comply with some, but not all of these conditions. The strength of the exposure driven functional model is the potential for testing specific hypothesis of the effect of many exposures on different stages or mutations. An example of such design would be the testing of the effect of continuing or stopping exposures in relation to the last stage of carcinogenesis in a prospective or globolomic design. If successful the exposure driven carcinogenic model and the use of functional genomics could improve the understanding of carcinogenesis and concomitantly the assessment of causality as part of systems epidemiology.