One important exception is nonetheless common in the case of local recurrence: recurrences of both well-differentiated and dedifferentiated liposarcoma tend to grow with an infiltrative pattern toward the surrounding structures, with vascular adventitia included. The higher probability of vascular resection in case of recurrent RPS, partly justified by the presence of postsurgical adherences, should therefore be kept in mind (Fig. 4.1, panel b).

When a retroperitoneal leiomyosarcoma has been diagnosed by preoperative biopsy, it should be considered that the tumor may originate from a major retroperitoneal vein. However, surgical management of leiomyosarcoma primarily arising from the IVC will not be discussed in this chapter.

Overall, resection of the IVC during RPS surgery is needed in a minority of cases (9 %) and even more rarely when the RPS does not directly arise from a vein [4].

In a recent international retrospective series of more than 1000 patients surgically treated at reference institutions for primary retroperitoneal sarcoma, the rate of IVC (or iliac vein) resection en bloc with the RPS was estimated to be 10.9 % [5].

In the multivisceral resection setting for primary RPS, excision of major abdominal vessels has been described to be associated with increased risk of postoperative complications, even after adjusting the risk for the total number of organs resected. This is particularly understandable for major abdominal veins (the inferior vena cava and iliac veins) since their resection may carry an increased risk of bleeding and/or fluid collection. Postoperative percutaneous drainage of any collection may be needed to avoid infection if vascular grafting has been performed. Moreover, stronger anticoagulation regimens after vascular surgery may further affect the risk of bleeding (Fig. 4.2) [6].

For the same reason, it is mandatory to achieve the safest vascular control when approaching a retroperitoneal mass. In very bulky masses, a generous midline incision may be extended either with a subcostal incision, or transversally to the flank, or sidelong to the inguinal ligament (Fig. 4.3, panel a). Right thoraco-phreno-laparotomy will enable adequate control of the retrohepatic IVC in the case of bulky disease in the upper right abdominal quadrant (Fig. 4.4). A good retractor will be very helpful in ensuring safe exposure and manipulation of major retroperitoneal vessels beneath a huge mass (Fig. 4.3, panel b).

An international series of 1007 primary retroperitoneal sarcoma patients with a median follow-up of 58 months produced the following outcomes: 5-, 8-, and 10-year overall survival rates of 67 %, 56 %, and 46 %; 5-, 8-, and 10-year crude cumulative incidence of local recurrence of 25.9 %, 31.3 %, and 35 %; and crude cumulative incidence of distant metastases of 21 %, 21.6 %, and 21.6 %, respectively. Tumor size, histologic subtype, malignancy grade, multifocality, and completeness of resection were significant predictors of outcome.

Histologic subtype is particularly relevant in surgical decision-making due to different patterns of outcome (Fig. 4.5). Dedifferentiated liposarcoma is the most common histology in the retroperitoneum, accounting for 35 % of all cases. Overall survival for dedifferentiated liposarcoma is estimated to be 43.9 % at 8 years. Deaths due to dedifferentiated liposarcoma are more related to the risk of local recurrence, which is over 40 % at 8 years, while the risk of distant metastases is less than 20 %.

Well-differentiated liposarcoma is the low-grade counterpart and accounts for 25 % of cases. Overall survival in well-differentiated liposarcoma has been estimated to be above 80 % at 8 years. As the metastatic risk is virtually nil for well-differentiated liposarcoma, disease mortality is related entirely to locoregional recurrences, observed as the only mode of failure in nearly one third of patients. This emphasizes the need for optimal initial surgical management of disease, preferably at experienced reference centers.

Leiomyosarcoma is the third histotype described in retroperitoneal sarcoma and is found in 20 % of cases. Leiomyosarcoma can also arise in the pelvis. The majority of purely retroperitoneal leiomyosarcomas can ultimately be found to originate from vessels, particularly from major retroperitoneal veins. Vascular leiomyosarcomas in the retroperitoneum most frequently arise from the IVC, while leiomyosarcomas have been described to originate from the renal vein and from the iliac, gonadal, and splenic veins (Fig. 4.6). Secondary involvement of the abdominal aorta by an IVC leiomyosarcoma is instead very uncommon (Fig. 4.7). Overall, retroperitoneal leiomyosarcomas have shown an 8-year overall survival rate of 40 %. As the risk of local recurrence in leiomyosarcoma is around 10 %, disease mortality in patients with retroperitoneal leiomyosarcoma is essentially related to metastatic spread, occurring in as many as 50 % of patients.

Solitary fibrous tumor (SFT) accounts for 6 % of retroperitoneal sarcomas. It is usually considered to have a good prognosis with an overall survival of 80 % at 8 years. The incidence of local recurrence and distant metastases is as low as 10 %. For this reason, solitary fibrous tumor has often been described as a benign entity. SFTs are in fact classified as “typical” and “malignant,” based on mitotic count (< and ≥4/10 high-power microscopic fields, respectively), the presence of necrosis, and nuclear polymorphism. A strong correlation between morphology and clinical course is, however, lacking, so that to date there is no way to predict the outcome of an SFT based on its pathologic features. Moreover, solitary fibrous tumors rarely show an abrupt transition from a conventional SFT to a high-grade sarcoma, also called “dedifferentiated” SFTs. These “dedifferentiated” lesions are aggressive soft tissue sarcomas. For this reason, virtually no solitary fibrous tumor should be considered purely benign, and prolonged follow-up is recommended for disease recurrence surveillance.