Solitary fibrous tumour of the kidney with sarcomatous overgrowth . Case report and review of the literature

Solitary fibrous tumour (SFT) rarely occurs in the kidney, with only one case exhibiting malignant behaviour. We report the case of a typical SFT of the kidney with sarcomatous overgrowth in a 34‐year‐old woman. This malignant component, grossly apparent as a nodular area arising in the context of the main tumour mass, consisted of CD34⁺ mitotically active atypical plump spindle‐ to epithelioid‐shaped cells, including pleomorphic multinucleated giant cells. A novel immunohistochemical finding was diffuse and strong S‐100 protein expression by sarcomatous cells. This should be kept in mind by pathologists to avoid confusion with other S‐100 protein‐positive malignant neoplasms.