Chemical carcinogenesis

In chemical carcinogenesis, the molecular mechanism of carcinogenic initiation of cells can be clearly demonstrated. The presence of carcinogenic substances in chimney smoke was described as early as 1775 by Percival Pott in England. Climbing boys, i.e. the boys who cleaned chimneys, were later frequently diagnosed with squamous cell carcinoma of the scrotal skin(chimney sweep cancer - occupational disease).

The number of chemical carcinogens is not yet manageable. In addition to the carcinogenic substances known for a long time (methylcholanthrene, benzpyrene, azo dyes), carcinogenic substances can be spread by food, exhaust gases and cigarette smoke. Another risk factor is chronic alcohol abuse. Most chemical carcinogens only act after enzymatic conversion, so they are procarcinogens. The most important chemical carcinogens belong to these 4 groups:

• Polycyclic aromatic hydrocarbons (PAC; see also MOAH, MOSH). The polycyclic aromatic hydrocarbons include e.g. 3,4-benzpyrene. This is produced by incomplete combustion of coal and oil and is therefore found in tobacco smoke, in the exhaust gases of internal combustion engines. It is probably the most important carcinogen in our environment. Other important carcinogens in this group are methylcholanthrene and dibenzanthrene.
• Aromatic amines: Already at the end of the 19th century, carcinomas of the urinary bladder were frequently observed in aniline workers. Among the aromatic amines are also: dimethylaminobenzene (butter yellow) and 2-acetaminofluorene (in experimental animals liver cancer).
• N-nitoso compounds (non-aromatic N-nitrosis compounds, especially nitrosamines) are formed in the stomach from nitrites and nitrates, i.e. from natural or preservative substances.
• Mycotoxins (the best known are aflatoxins which can be found in mould in various types of mould. Food-components can be proved in the mold)

Other chemical carcinogens are inorganic substances such as lead, arsenic, asbestos and the alkylating substances used in cancer therapy.

1. Appel KE et al (1990) Chemical cancerogenesis: definitions of frequently used terms. J Cancer Res Clin Oncol 116:232-236.