Light micrograph of a section of human skin tissue showing retiform haemangioendothelioma (RH). It is a rare vascular neoplasm of intermediate or borderline malignancy involving the skin and subcutaneous tissue. This rare slow-growing tumour usually forms on or under the skin of the arms, legs and trunk. The tumour itself has blood vessels that branch out like a tree. Retiform haemangioendotheliomas can spread to nearby tissue and often returns after treatment. They mostly occur in young adults, but sometimes they can affect children.