Epidemiological studies indicate that occupational exposure to
coal tar may lead to an increased risk of lung, scrotum and
skin cancer. Furthermore, studies with laboratory rodents show carcinogenicity of
coal tar after dermal application. This effect may be attributable to
polycyclic aromatic hydrocarbons (PAH), which are ubiquitous
coal tar constituents. Absorbed PAH can be metabolised to reactive derivatives that bind to
DNA. These PAH-
DNA binding products are thought to be involved in PAH-induced
carcinogenesis. However, no clearly increased
skin cancer incidences have been reported in
psoriasis patients who have been exposed to therapeutically high doses of
coal tar. To determine whether patients treated with
coal tar actually have an altered risk of cutaneous
malignancies, we suggest that further controlled studies and experiments are necessary. Future research should also focus on the possibility of increased risks of developing internal
malignancies.