Chapter 27: Retroperitoneal Sarcomas

INTRODUCTION

Approximately 15% of soft tissue sarcomas (STS) occur in the retroperitoneum, and thus, there are only approximately 1600 new retroperitoneal sarcomas (RPS) in the United States per year.¹ In large series, the average age is between 50 and 60 years old and there are equal numbers of men and women.^2-4 RPS are frequently asymptomatic until reaching large sizes, and thus the average size of tumors is often greater than 10 to 15 cm. The optimal local therapy for RPS includes surgical resection with negative microscopic margins, but many if not most tumors cannot be removed in this fashion. Even with complete surgical resection, local recurrence rates can approach 50% or greater. An important aspect of RPS is that even though many of these tumors are large and high grade, the metastasis rate is significantly lower than that of extremity and truncal tumors, with the most common sites of metastasis being the lung and liver.⁵ Thus, local recurrence is the leading cause of death in RPS patients. The role of preoperative or postoperative radiation therapy in reducing local recurrence of extremity and trunk STS is firmly established by prospective, randomized trials.^6-8 In contrast RPS are generally large and abut radiation-sensitive organs such as the kidney, liver, and small bowel, making the delivery of adequate doses of preoperative radiation difficult.⁹ The role of adjuvant chemotherapy in reducing local recurrence rates in any location is modest at best.¹⁰ More recent studies of more aggressive surgery and advanced radiation techniques have suggested that local recurrence can potentially be reduced, but these strategies are debatable. Newer chemotherapies and targeted agents may also play a role in the reduction of local recurrence rates. This chapter summarizes the current management of RPS with emphasis on surgical resection and radiation therapy.

HISTOLOGY

In fact, the histologic grade of STS is determined by morphological features including necrosis, mitoses, and degree of differentiation.¹¹ The World Health Organization (WHO) has defined over 50 subtypes based on the histologic appearance of the tumor tissue.¹² About two-thirds of RPS are either liposarcomas or leiomyosarcomas, with the remaining tumors distributed among a large variety of other histologic subtypes.⁴ It should be noted that each histologic subtype of STS may have a unique tumor biology, radiological appearance, and clinical behavior. For example, well-differentiated liposarcomas, chromosome 12q is often amplified resulting in overexpression of MDM2 and CDK4.¹³ These tumors have a characteristic appearance on computed tomography (CT) scans as large fatty tumors with internal septations (Fig. 27-1A).¹⁴ As these well-differentiated liposarcomas enlarge, they can develop more solid areas in a process known as dedifferentiation (Fig. 27-1B). In a study by the M.D. Anderson Cancer Center, CT scan features accurately identified 60 out of 60 (100%) of well-differentiated liposarcomas but was less accurate in determining areas of hypercellular well-differentiated liposarcoma from ...