Spitz tumours and mimickers.

Since their initial description in 1948, Spitz tumours have always been a challenge in the field of dermatopathology and paediatric pathology. Advances in molecular pathology have confirmed they are associated with specific anomalies, mainly gene fusions. They display a wide range of clinical presentations and histological subtypes. Most cases are Spitz nevi and very few lesions match the criteria to be diagnosed as atypical Spitz tumours. Even fewer are labelled as Spitz melanomas. Follow-up studies of genetically characterized cases have repeatedly confirmed that, even if the regional lymph node is involved, the overall outcome remains favourable. The aims of this review are to cover the variety of morphological presentations of Spitz tumours and illustrate the most rare subtypes. When possible, we have pointed out the potential trends between some unusual morphological features and the frequently associated genetic drivers. Spitz tumours have many differential diagnoses, the main being superficial spreading melanoma, with overlapping morphological features in early lesions. Essential clues to discriminate Spitz from mimickers have been listed and illustrated.