The widespread occurance of cancer and its apparent lack of a cause has led to a plethora of myths spanning from a "cancer personality" in the 1970's to mobile phones today. The dissertation introduces some of the theoretical principles of cancer which lifts the veil on the mysteries surrounding its causes. The central issue addressed is whether genetic instability above the background level is necessary to account for the levels of cancer seen. In doing so, it touches on the idea that we are all born with mutations - from the very first division at the embryonic stage we begin acquiring them. This occurs even in a perfect environment without mutagens or any environmental stressors. The common conception, of the cells working together for a common goal is reversed. The body can be viewed as a vast community of selfish cells which are constantly competing for resources in a process analogous to Darwinian natural selection.
Evolution at the organism level has resulted in a comprehensive disciplinary system to keep the masses in check. Any individual which
hints at crossing out of line is sentenced to the biochemical equivalent of imprisonment or the death sentence. However despite the organism's iron tight grip on the individual cell, it is clear that we all carry the prerequisites of cancer around with us. We will all be diagnosed with "cancer" at some point, the reason it only kills a third is that most die of something else first. Even if we live a perfect life without any disease - there is always the self which is imperfect. This dissertation explains in detail how we are gaining a deeper understanding which offers the hope that in the near future we will no longer need to live in fear of the unknown.
Table of Contents
Introduction
How many mutations are required to produce a human cancer cell?
Sequence data
Epidemiology
In vitro data
Histopathology
Is genetic instability necessary to acquire sufficient mutations?
The mutator phenotype hypothesis
Arguments which undermine the calculations’ assumptions
Clonal evolution and natural selection
Arguments for the calculations validity
Tissue Biology
Epigenetics
CpG island promoter hypermethylation
Global CpG hypomethylation
Does genetic instability accelerate tumour progression?
Cell clone ecology hypothesis
Mathematical assessment
Lab based test
Clinical data
Sequence Data
Implications for therapy
Conclusion
Research Objectives and Thematic Focus
This work aims to investigate the necessity and impact of genetic instability in cancer progression by fractionating the problem into key constituent parts, such as the required mutation load and the role of cellular evolution. It evaluates whether increased genetic instability is essential for tumorigenesis or if it serves as an accelerating mechanism influenced by environmental and epigenetic factors.
- The minimum number of genetic mutations required for human tumorigenesis.
- The necessity of a "mutator phenotype" for acquiring these mutations.
- The influence of epigenetic alterations and tissue-specific biology on cancer evolution.
- Mathematical and theoretical modeling of clonal selection and mutation rates.
- The potential for novel drug targets based on the understanding of these driving forces.
Excerpt from the Book
The mutator phenotype hypothesis
As described in the last section, tumorigenesis is thought to proceed via a multistep stochastic pathway. It has been suggested by Loeb et al (1991) that the background mutation rate under normal physiological growth conditions may be too low to allow these steps to occur in the fixed timeframe of the human life span. An updated version of the original estimation which led to this proposal is presented here (Beckman and Loeb 2005): The stem cells thought to give rise to tumours have a rate of mutation between 10^-9 and 10^-11 per nucleotide locus per division. The maximum number of stem cell generations in a human lifetime is thought not to exceed 10^4 and only a very small fraction of somatic cells are stem cells. Assuming six independent, specific mutations are required to accomplish the six rewiring’s mentioned previously, the chances against any stem cell in a human developing sufficient mutations are astronomical. Even when taking the minimum epidemiological estimate of 2 mutations being necessary, the estimated probability of developing a cancer per individual per lifetime would be far less than the levels observed.
To account for this discrepancy they suggested that an accelerating mechanism may be required. They posited that raised genetic instability manifesting as a “mutator phenotype” could boost the rate at which variation is produced thereby shortening the time between tumorigenic steps and allow cancer to develop at the rates seen.
Summary of Chapters
Introduction: Provides the foundational context of cancer as a multistep evolutionary process and introduces the debate regarding the necessity of genetic instability versus natural selection.
How many mutations are required to produce a human cancer cell?: Evaluates data from sequencing, epidemiology, and in vitro experiments to estimate the number of rate-limiting steps in carcinogenesis.
Is genetic instability necessary to acquire sufficient mutations?: Critically assesses the mutator phenotype hypothesis, exploring alternative explanations like tissue biology, epigenetics, and clonal dynamics.
Does genetic instability accelerate tumour progression?: Analyzes whether genetic instability acts as a beneficial trait for cancer cells through mathematical models and clinical observation.
Keywords
Tumorigenesis, genetic instability, mutator phenotype, clonal evolution, natural selection, cancer hallmarks, epigenetic alterations, CpG methylation, mutation rate, tissue biology, stochastic pathway, multistep model, cancer therapy, drug targets.
Frequently Asked Questions
What is the central focus of this research?
The research explores the necessity and functional role of genetic instability in the progression of cancer, examining whether it is a strictly required driver or an accelerating factor.
What are the primary themes discussed?
The themes include the number of mutations required for tumorigenesis, the mutator phenotype hypothesis, the impact of epigenetic silencing, and the evolutionary dynamics of cancer cells.
What is the core research question?
The primary inquiry is whether raised genetic instability is necessary to acquire sufficient mutations for cancer development or if other biological mechanisms can account for observed cancer rates.
Which methodology is employed?
The study utilizes a theoretical synthesis of existing scientific literature, mathematical models, and experimental data to break down the problem of tumor evolution into manageable, examinable components.
What is addressed in the main body?
The main body systematically evaluates mutation counts, the role of natural selection in clonal expansion, the influence of epigenetic changes like CpG methylation, and clinical evidence for genetic instability.
Which keywords best characterize this work?
Key terms include Tumorigenesis, Genetic Instability, Mutator Phenotype, Clonal Evolution, and Epigenetics.
How do epigenetic modifications influence the debate on genetic instability?
Epigenetic changes, such as promoter hypermethylation, provide an alternative mechanism for gene silencing that reduces the total reliance on genetic mutations, potentially weakening the argument that a mutator phenotype is strictly necessary.
What does the "immortal coil" hypothesis contribute to the discussion?
It proposes a mechanism for minimizing mutation rates in stem cells, suggesting that tissues have built-in defenses against genetic instability, which challenges current models that often overestimate mutation rates.
- Quote paper
- Pascal Kaufmann (Author), 2011, How many mutations are required to produce a human cancer cell?, Munich, GRIN Verlag, https://www.hausarbeiten.de/document/168293
