Carcinogenesis

Definition
This section has been translated automatically.

Development of malignant tumours. It begins with the transformation of a physiological cell into a tumor cell. It is likely that the majority of cancers are caused by genetic changes (mutagenesis). It is also known for certain that a carcinoma develops slowly, as a complex mix of influences from the environment (e.g. UV radiation; see below photocarcinogenesis), lifestyle (smoking) and heredity (mutated alleles). This process can last for years or decades.

Classification
This section has been translated automatically.

A hypothetical three-step model of carcinogenesis serves to better understand the process and is divided into 3 developmental stages:

Initiation
Promotion
Progression.

Initiation is the first step in carcinogenesis, in which a cell undergoes a mutation triggered by a carcinogen (see below photocarcinogenesis). If this mutation is not eliminated by DNA repair or the cell is not switched off by apoptosis, it is irreversible. For carcinogenesis it is important that this mutation is present in a gene that is responsible for controlling the cell cycle and cell division, e.g. in one of the tumour suppressor genes. Mutated tumour suppressor genes are called oncogenes.
During promotion, a growth stimulus acts on the altered cell. This growth stimulus can emanate from the so-called "non-genotoxic carcinogens", such as hormones in breast cancer (promotion of growth stimulus via growth factors). Inflammatory processes can also exert growth stimuli on the cell (e.g. in the case of long-term persistent ulcus cruris, also in Crohn's disease). The initiated cell passes on its DNA damage to the daughter cell through cell proliferation. The proliferating cell has an unstable DNA, which increases the risk of further mutations in tumour suppressor genes.
During progression, the cells of the preneoplastic area experience further mutations in tumour suppressor genes; numerous tumour suppressor genes are converted into oncogenes. Now the actual malignant transformation takes place. Under different clinical pictures the carcinoma in situ (see below PIN; CIN, keratosis actinica) is formed which sooner or later develops into an invasive carcinoma.