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

Abstract

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

Keywords: adult rhabdomyosarcoma; extraosseous Ewing sarcoma; extraosseous osteosarcoma; perivascular epithelioid tumour; retroperitoneal sarcoma; ultra-rare sarcoma.

Figure 1

Primary retroperitoneal benign, AML arising from the kidney (blue arrows, Panel (A)) and primary retroperitoneal malignant PEComa-NOS arising from the rectosigmoid mesentery (blue arrows, Panel (B)). Both show similar CT characteristics, including density inconsistent with fat (−52 and −39 Hounsfield units, respectively) and well-circumscribed borders apart from the organ of origin (Kidney in Panel (A), and sigmoid in Panel (B)). While both AML and PEComa commonly arise from the kidney and perinephric fat, AML rarely, if ever, arises directly from the retroperitoneal tissues. Retroperitoneal core biopsy confirmed the diagnosis in both cases. The AML was managed with preoperative angioembolization and marginal excision of the left kidney and retroperitoneal tumour en bloc (R0 resection). The malignant PEComa-NOS was managed with radical resection, including rectosigmoid and low anterior resection, clearance of the retroperitoneal tissues above the aortoiliac axis, and right hemi-colectomy due to cecal abutment (R0 resection).

Figure 2

Primary retroperitoneal extraosseous Ewing sarcoma (blue arrows) before (Panel (A)) and after (Panel (B)) neoadjuvant VDC/IE, with 60% tumour volume reduction. This patient underwent R0 resection of RPS with en bloc resection of the anterior wall of the aorta and inferior mesenteric artery. Due to good response from chemotherapy, the left ureter, left kidney, and left colon were successfully preserved.

Figure 3

Primary retroperitoneal extraosseous osteosarcoma (blue arrows) axial (Panel (A)) and coronal (Panel (B)) views. This tumour shows CT characteristics including a deep-seated pelvic tumour with significant calcification matrix, and invasion into the rectum, prostate, pelvic floor muscles, and left pelvic sidewall. This patient underwent R0 resection of RPS with pelvic exenteration including en bloc extralevator abdominoperineal resection, cystoprostatectomy, clearance of ischiorectal fossa and ischial tuberosity without bony involvement.