REtroperitoneal SArcoma Registry (RESAR): Prospective Collection of Primary Retroperitoneal Sarcoma Patient's Data, Radiological and Pathological Material for the TransAtlantic Retroperitoneal Sarcoma Working Group

Retroperitoneal sarcomas (RPS) are rare tumors accounting for 10-15% of all soft tissue sarcomas (STS). They arise between retroperitoneal organs and among vital structures (ie major abdominal vessels) in an anatomical compartment that is not readily accessible by physical examination. Four main histotypes account for about 80% of all cases: well-differentiated liposarcoma (WDLPS), dedifferentiated liposarcoma (DDLPS), leiomyosarcoma (LMS) and solitary fibrous tumor (SFT).

Compared to sarcomas at other anatomic sites, RPS are burdened by a higher local recurrence (LR) rate (50% at 5 years) and a poorer overall survival (OS) rate (50% at 5-years). The natural history of RPS as a whole group reflects the strong tendency of lipomatous tumors (WDLPS and DDLPS, which account for about 50% of RPS) to recur locally. Indeed, outcome of primary RPS is highly related to the histological subtype.

WDLPS are characterized by a relatively lower LR rate, negligible metastatic potential and a favorable overall survival. These tumors however, still may recur locally even years after the primary resection. Intermediate grade DDLPS are characterized by a strong tendency to recur locally and low metastatic potential. High grade DDLPS has a high risk of both local recurrence and distant metastasis. LMS are usually intermediate or high-grade tumors with a strong tendency to develop distant metastasis; with an adequate resection, it is relatively common to obtain a durable local control. Classic SFT usually fare well after surgery, with a low rate of local recurrence and distant metastasis.

Historically, surgery emerged as the only potentially curative option in the localized setting. In the last few years there has been lively debate as to how far should a surgeon resect in order to obtain a margin that could be considerate adequate. This issue is particularly challenging in this anatomical compartment where widening the surgical margins means resecting adjacent organs.

Since 2002 an 'extended' surgical approach has been proposed for primary RPS patients. The concept was that surgical margins could be improved by encompassing the tumor with en-bloc resection of adjacent organs. The aim was to obtain reduced local recurrence and improved survival. This approach has proven to be effective. In particular, this surgical approach has been supported by an experimental model, retrospective comparisons, pathology studies demonstrating adjacent organ involvement, and reports of high rates of residual tumor at re-excision after conventional (non-extended) primary surgery. Finally, this approach has been shown to be safe after both short and long term follow-up.