Novel and emerging skin carcinomas and adnexal tumours

Epidermal and adnexal tumours of the skin constitute a complex and heterogeneous group of neoplasms, with distinct morphology and behaviour. Over recent years, the genetic characterization of such neoplasms has enabled the identification of several new tumour entities. Among such emerging skin tumours, it is noteworthy that the majority harbour phenotypic and molecular similarities with entities already well established in other organs. Notably, over the last decade, several sweat gland tumours analogous to neoplasms of the salivary glands have been reported. More recently, among poorly differentiated skin carcinomas, several distinctive tumour entities defined by recurrent genetic alterations previously reported in other organs notably the lung have been identified. Finally, a couple of recurrent oncogenic events not previously described in other organs have recently been documented in skin epithelial tumours allowing for the refinement of the diagnostic criteria of established tumour entities and the identification of novel ones. In the present review, we aim to provide an overview of the main emerging skin epithelial tumours, with particular emphasis on what the field of dermatopathology can learn from the oncogenic mechanisms already identified in other organs.