The skin is the largest organ of the human body and performs a number of very important functions for the body. 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.