Practical Management of Adult Ultra-Rare Primary Retroperitoneal Soft Tissue Sarcoma: A Focus on Perivascular Epithelioid Tumours and Extraosseous Ewing Sarcoma

With the exception of well-differentiated liposarcoma, dedifferentiated leiomyosarcoma, solitary fibrous tumour, malignant peripheral nerve sheath and undifferentiated pleomorphic sarcoma, majority ≈70 histologic subtypes retroperitoneal sarcoma are defined as ‘ultra-rare’ sarcomas, with an incidence ≤1–5/1,000,000 persons/year. For most these ultra-rare RPS subtypes, diagnosis treatment follows international guidelines for management more common histologies, en bloc surgical resection mainstay curative treatment, enrolment in clinical trials where possible. Because is heavily driven by histology, surgeon must be familiar specific issues related to subtypes. Expert radiological reviews required differentiate similarly presenting tumours surgery can avoided (e.g., angiomyolipoma), or upfront systemic therapy indicated extraosseous Ewing’s sarcoma). Thus, all sarcomas should occur at a referral centre, multidisciplinary team experts dedicated medical rare tumours. In this focused review, we highlight how primary histologies perivascular epithelioid cell tumour (PEComa), Ewing (EES), osteosarcoma (EOS), rhabdomyosarcoma (RMS) critically diverge from