Objectives: Collision tumours are rare situations characterised by the coincidence of two different skin neoplasms in the same lesion. Methods: We have analyzed 41 collision skin tumours from one department in the clinical-dermoscopic-histopathologic correlations. Results: We present 41 collisions tumours. The mean age of our patients was 67.9 years, the mean diameter of the lesion was 11.6 mm. The most frequent locations were trunk (27 lesions) and head/neck (11 lesions). The collisions were classified as benign/benign (13 cases), benign/malignant (25 cases) and malignant/malignant (3 cases). The most frequent participants were seborrheic keratosis (24 cases), malignant melanoma (17 cases), melanocytic nevus (14 cases), basal cell carcinoma (12 cases) and heamangioma (10 cases). Thirty cases were of "dominant/minor" type and 11 cases of "half to half" type. Malignant tumours were a part of 28 collisions; these lesions were larger, patients were older and the malignant part was dominant in most cases. More than half of the collisions were unexpected by the initial clinical examination. Six collisions were missed by the initial histopathological examination. Conclusions: Collision tumours can be missed by clinical or even histopathological examination. Dermoscopy is very helpful in the recognizing of difficult cases and cooperating with the histopathologist.

Department of Dermatovenereology Faculty of Medicine and Teaching Hospital Charles University Pilsen Czech Republic

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