The skin is the largest organ of the human body and has a number of very important functions. Due to the pathological changes that can be observed on its surface, it is also of great importance in the detection of malignant tumours affecting internal organs. Scientists have found many correlations between existing malignancies and changes on the skin surface, describing them as disease entities, e.g. glucagonoma, Paget's disease, keratosis nigricans, Birt-Hogg-Dubè syndrome, basal cell nevus syndrome, Bazex syndrome, carcinoma syndrome.