Rarely metastasizing soft tissue tumours.

Soft tissue tumours that rarely metastasize have been afforded their own subcategory in recent WHO classifications. This review discusses the nature of these tumours and the difficulty in constructing usefully simple classifications for heterogeneous and complex groups of tumours. We also highlight the specific rarely metastasizing soft tissue tumours that have been recently added to the WHO classification (phosphaturic mesenchymal tumour, pseudomyogenic haemangioendothelioma) and those entities where there have been recent important defining genetic discoveries (myxoinflammatory fibroblastic sarcoma, solitary fibrous tumour, myoepitheliomas).