Immunosuppression-associated soft-tissue tumours

Immunodeficiency and therapeutic immunosuppression inform the pathogenesis of certain soft tissue tumours, namely Kaposi sarcoma (KS) and Epstein-Barr virus (EBV)-associated smooth muscle tumours. KS comprises a group of clinical categories associated with local or systemic immunodysregulation: sporadic/classic KS, endemic (African) KS, epidemic (AIDS-related) KS, and iatrogenic (transplantation-associated) KS. Histologically, KS lesions progress from early (patch) stages, comprising networks of bland vascular proliferations, to later (plaque) stages, wherein spindle cells proliferate between vascular structures, and finally to the nodular (tumour) stage, which may show fascicles of intersecting spindle cells and PASD-positive hyaline globules. By immunohistochemistry, KS shows lymphovascular differentiation. EBV-associated smooth muscle tumours comprise a rare subset of smooth muscle tumours that typically occur in children with HIV/AIDS and adults following solid organ transplantation. They can occur in peripheral soft tissues, intracranially, or in visceral sites. Multiplicity is common and presumably a result of multiple infection events rather than metastasis from a primary site. Histologically, the differential diagnosis is limited to other smooth muscle tumours. These indolent tumours often persist despite therapy but rarely metastasize. Mortality usually results from the underlying disease process.