[External factors catalyzing the development of tumours or providing protection against them]. / Zevní vlivy podminující vznik nádoru nebo ochranující pred jejich vznikem.

The number of malignant diseases increases and the question is why. Why is there an increasing incidence of certain cancers and why an increasing number of people dies from them? We do not have a clear answer to these questions. We just know that a development of cancer depends on certain internal predispositions as well as external conditions. We are unable to change our genetic predisposition but we are able, to some extent, influence the intensity of external factors. This paper summarizes information on the effects of external environment on the development of malignant diseases.