The process by which normal, healthy cells transform into cancer cells is termed carcinogenesis or oncogenesis. The development of a malignant tumour in otherwise healthy tissue is the result of a complex series of events beginning with a single cell that has acquired malignant properties through cellular DNA damage.
Errors in the DNA sequence interrupt the genetic codes that govern the structure and function of the affected cell. The survival and proliferation of a cell with DNA damage, dividing to give rise to two daughter cells, each then capable of dividing, eventually results in a population of clones with similar genetic errors and malignant properties.7, 16, 19
Before malignant cells can cause symptoms or be detected, successive generations of daughter cells must divide and double the size of the clonal population approximately 30 times. At this point, the tumour will likely measure one cubic centimetre, weigh about one gram and comprise one billion cells.5, 7
Most current theories of carcinogenesis characterise it as a multi-step process involving initiation, growth, promotion, conversion, propagation, invasion and metastasis.7, 9, 13
Carcinogens are defined as agents capable of initiating the development of malignant tumours by inducing cellular genetic changes. The transformation of a normal cell to a malignant cell is thought to be due to successive and cumulative exposures to carcinogens and other factors over the course of decades. Most human cancers result from exposure to environmental (or exogenous) carcinogens. Other carcinogens that cause malignant transformation include a broad group of factors from within the body, termed endogenous factors.6, 19
Access a current text and/or the Cancerquest website20, and:
- Summarise the three stage model of carcinogenesis.
- List two examples each of exogenous and endogenous carcinogens.
- Provide an explanation of how the carcinogens identified in the previous activity act to initiate the development of a malignant tumour.