Soft-tissue sarcomas are a rare heterogeneous group of tumors that arise from mesenchymal cells. They account for approximately 1% of all solid malignant tumors in adults and about 7% in children. There are more than 80 different histologic subtypes of soft tissue sarcoma, with variable presentations, behavior, and long-term outcomes (Table 1).1 Soft tissue sarcomas can occur at any age and any location in the body, but maximum peak is 40-60 years of age and most frequent locations are in the extremities, chest wall, and retroperitoneum. The most common soft tissue sarcoma subtypes in adults are liposarcoma, leiomyosarcoma, and undifferentiated pleomorphic sarcoma, while the most common in children is rhabdomyosarcoma.2

Soft tissue sarcomas typically present as a painless slowly growing soft tissue mass although symptoms may eventually develop due to mass effect on adjacent nerves, vessels, joints, and other structures. The most common anatomic locations for soft tissue sarcomas of musculoskeletal origin are the lower extremities (40%-50%), upper extremities (15%-20%), chest wall (20%), retroperitoneum (10%-15%) and head/neck (10%). The vast majority of soft tissue sarcomas are deep to the superficial muscular fascia.3

Although imaging with MRI has a vital role in early diagnosis, as it accurately determines the primary tumor size, location, and relationship to adjacent structures, histopathologic analysis from tissue sampling remains the gold standard for diagnosis of soft tissue sarcomas and determines the sarcoma subtype and grade.4 Prognosis is then determined through the combination of the histologic subtype, the tumor's grade, the size, and depth of invasion, the stage of the disease at initial presentation, and patient age.5

Treatment for soft tissue sarcomas is typically multidisciplinary and includes surgery, radiation therapy, and chemotherapy. For patients with localized disease who are surgical candidates, the goal is complete excision with wide margins, with adjuvant or neoadjuvant chemoradiotherapy dictated by tumor histology, size, and location. Chemotherapy (anthracycline and ifosfamide based) is a mainstay of treatment for metastatic soft tissue sarcoma, although more specific treatments such tyrosine kinase inhibitors and immunotherapy may be used in specific subtypes.6

Prognosis for soft tissue sarcoma varies, with a 5-year survival rate of 82% for localized disease, 60% for locally advanced disease, and 17% for metastatic disease, at initial presentation.7 The prognosis and varying clinical behavior of these tumors is closely associated with histological grade. The American Joint Committee on Cancer (AJCC) staging system incorporates includes histologic tumor grade in addition to the standard tumor, node, metastasis (TNM) classification, reflecting that the same histologic grade in different subtypes likely has similar biological behavior; with greater risk of recurrence, distant metastases and fatal outcome in patient with high grade histology.8

Treatment of soft tissue sarcoma requires a high level of expertise due to its rarity and heterogeneity and numerous studies have showed improved outcomes in tertiary centers with devoted multidisciplinary teams comprising oncologists, orthopedic surgeons, radiologists, and pathologists.9 Sarcomas centers have been shown to perform more diagnostic procedures, which may contribute to more personalized therapy regimens and better outcomes. Interest in improving diagnosis and treatment with imaging has led many groups to investigate the utility of FDG PET in not only the initial diagnosis but also in the staging, restaging, and monitoring of response.10

Over the past 20 years, the role of FDG PET in sarcoma evaluation has evolved significantly. In 2003, a meta-analysis of 15 studies that concluded that FDG PET has good discriminatory ability for differentiating benign and malignant soft tissue lesions, and may be helpful in tumor grading, but is inadequate for discriminating between low-grade malignant and benign soft tissue lesions.11 More than a decade later, a systematic review of 34 high-quality studies concluded that PET is an important contributor to sarcoma grading, prognostication, and evaluation of treatment response; helps differentiate between low-grade and high-grade sarcomas; and facilitates early identification of patients who will respond to adjuvant or neoadjuvant therapy.12

The expanding role of FDG PET in soft tissue sarcoma has led to its incorporation into clinical oncology guidelines. The National Comprehensive Care Network (NCCN) guidelines state that for FDG PET may be useful for staging, prognostication, and determining response to systemic therapy. In addition, PET imaging prior to biopsy can allow targeting of metabolically active areas of tumor and help prevent nondiagnostic sampling of necrotic areas. The NCCN states that FDG PET may be useful to differentiate between well-differentiated and dedifferentiated liposarcoma; to stage rhabdomyosarcoma; to distinguish between benign and malignant peripheral nerve sheath tumors; and to evaluate regional lymph nodes in soft tissue sarcoma subtypes with risk for nodal metastases, including angiosarcoma, clear cell sarcoma, epithelioid sarcoma, and rhabdomyosarcoma, among others.13