Screening and diagnosis
Currently, there are no screening tests for soft-tissue sarcomas. Since the majority of patients with soft-tissue sarcoma have lesions arising in the extremities or superficial trunk, most of the comments here apply to soft-tissue lesions in those sites. A separate algorithm is usually employed for the evaluation of a primary retroperitoneal mass or visceral sarcoma.
Physical examination should include an assessment of the size of the mass and its mobility relative to the underlying soft tissues. The relationship of the mass to the investing fascia of the extremity (superficial vs deep) and nearby neurovascular and bony structures should be noted. Site-specific neurovascular examination and assessment of regional lymph nodes should also be performed.
Any soft tissue mass in an adult extremity should be biopsied if it is symptomatic or enlarging, is > 5 cm, or has persisted beyond 4 to 6 weeks.
Percutaneous tissue diagnosis can usually be obtained by percutaneous core biopsy for histology. The needle track should be placed in an area to be excised or that can be encompassed in adjuvant radiotherapy fields if they are to be used. In most instances, when an experienced histopathologist examines the specimen, a diagnosis of malignant soft-tissue sarcoma can be made. Fine needle aspiration (FNA) is often viewed as a suboptimal method of establishing an initial diagnosis of soft-tissue sarcoma. Histology is usually preferred to cytology because more tissue is obtained, which allows for a more accurate delineation of tumor type and grade. FNA is a less-invasive means to confirm recurrence, however. Percutaneous tissue diagnosis is preferred to facilitate subsequent treatment planning and to permit surgical resection to be performed as a one-stage procedure.
In some cases, an adequate histologic diagnosis cannot be secured by percutaneous means. Open biopsy is indicated in these instances, with the exception of relatively small superficial masses, which can be easily removed by excisional biopsy with clear margins.
Biopsies should be incisional and performed with a longitudinal incision parallel to the long axis of the extremity. This approach facilitates subsequent wide local excision of the tumor, and the incisional scar results in minimal difficulties in wound closure. It also facilitates inclusion of any scars within the area of the tumor in adjuvant radiation fields without the excessive morbidity of large-field radiotherapy planning. The incision should be centered over the mass at its most superficial location. Care should be taken not to raise tissue flaps. Meticulous hemostasis should be ensured after the biopsy to prevent dissemination of tumor cells into adjacent tissue planes by hematoma.
Retroperitoneal or intra-abdominal mass
Biopsy of primary retroperitoneal soft-tissue masses is generally not required for radiographically resectable masses, nor is biopsy recommended for suspected GISTs. The circumstances under which percutaneous or preoperative biopsy of retroperitoneal masses should be strongly considered include:
• tissue diagnosis for radiographically unresectable disease
• clinical suspicion of lymphoma or germ-cell tumor
• tissue diagnosis for neoadjuvant treatment, including radiotherapy and/or chemotherapy
• suspected metastases from another primary tumor.
Primary tumor imaging
Optimal imaging of the primary tumor depends on the anatomic site. For soft-tissue masses of the extremities, MRI has been regarded as the imaging modality of choice because it enhances the contrast between tumor and muscle and between tumor and adjacent blood vessels and also provides multiplanar definition of the lesion. However, a study by the RDOG that compared MRI and CT in 183 patients with malignant bone and 133 patients with soft-tissue tumors showed no specific advantage of MRI over CT from a diagnostic standpoint.
For pelvic lesions, the multiplanar capability of MRI may provide superior single-modality imaging. In the retroperitoneum and abdomen, CT usually provides satisfactory anatomic definition of the lesion. Occasionally, MRI with gradient sequence imaging can better delineate the relationship of the tumor to midline vascular structures, particularly the inferior vena cava and aorta. In the future, MRI–CT fusion techniques may facilitate treatment planning using conformal radiotherapy techniques.
More invasive studies, such as angiography and cavography, are almost never required for the evaluation of soft-tissue sarcomas. The role of PET scan in sarcoma management is not well defined. For example, in metstatic disease, higher quality images can be obtained with a contrast CT than with a PET/CT, which uses less optimal CT for registration of images with PET images. There may be selected cases in which PET can be useful, particularly in patients who cannot tolerate IV contrast for CT scan or MRI.
In particular, if the lack of IV contrast uptake as a sign of a responding tumor is taken into account, contrast-enhanced CT scans appear to yield results similar to PET scans in patients with GIST.
Imaging for metastatic disease
Cost-effective imaging to exclude the possibility of distant metastatic disease depends on the size, grade, and anatomic location of the primary tumor. In general, patients with low-grade soft-tissue sarcomas < 10 cm or intermediate-/high-grade tumors < 5 cm in diameter require only a chest x-ray for satisfactory staging of the chest. This reflects the fact that these patients are at comparatively low risk of presenting with pulmonary metastases. In contrast, patients with very large (≥ 10 cm) low-grade tumors or high-grade tumors ≥ 5 cm should undergo more thorough staging of the chest by CT.
Patients with retroperitoneal and intra-abdominal visceral sarcomas should undergo single-modality imaging of the liver to exclude the possibility of synchronous hepatic metastases. The liver is a common site for a first metastasis from these lesions. Only rarely does PET appear to be indicated, in particular for patients with contrast allergies who cannot be staged definitively preoperatively with CT or MRI.