The standard bone scan is widely used in oncology for staging the skeleton for the presence of bony metastases. Sarcomas generally show osteoblastic behavior and are less likely to show lytic metastases. Often, as in the case of bone tumors, they show either a blastic or lytic appearance. For soft tissue masses, the bone scan is a standard part of disease staging. Patients with bony metastases show increased uptake in typical metastatic decrease patterns in the axial skeleton and extremities. The presence or absence of uptake is often diagnostic in separating more benign or locally aggressive tumors from malignant types. Bone scans also have special utility in primary bone tumors. These tumors form malignant osteoid matrices that are undergoing disordered calcification; therefore, they are ^99mTc-MDP avid (Fig. 23.1). Both the osteosarcomas and some chondrosarcomas with osteoblastic differentiation contain malignant osteoid. Ewing sarcomas cause bone destruction and reactions that result in bone scan positivity. Primary bone tumors have frequent bone metastases and can present with skip lesions in the affected bone. The osteosarcomas frequently have bone metastases, but bone scan positive appearance in multiple sites is common in Ewing sarcoma. In this latter group of tumors, metastases are often present at the time of diagnosis in both bone and soft tissue PNET primary tumors.

The bone scan is also a sensitive method for indentifying osteosarcoma pulmonary metastases (Fig. 23.2). These are often highly ^99mTc-MDP avid. Some clinicians use the relative decrease in bone scan uptake in pulmonary metastases as an indicator of treatment response and suitability for wedge resection metastasectomy. In osteosarcoma patients with ­limited pulmonary metastasis, this procedure has been shown to increase disease-free survival [17]. The ^99mTc-MDP scan has been reported to contribute to the diagnosis of bone ­forming malignant tumors by revealing unusual sites and presentations. As such, in these individuals, similar to primary bone tumor patients, the ^99mTc-MDP bone scan is likely a means of monitoring treatment response. In these patients, a decrease in malignant osteoid matrix calcification would indicate a response to treatment in this cellular portion of the tumor. The bone scan appearance in metastatic disease, as with other tumors, can also underestimate the extent and severity of skeletal metastases. In these cases, the metastases involving the bone may only be apparent when a cortical reaction occurs. Subsequent other whole body surveys such as CT or [¹⁸F]FDG PET may provide a complimentary picture of the extent of diseased skeleton [18].

²⁰¹TI-Chloride as a nonspecific tumor imaging agent has been described for use in many tumors, including sarcoma. Most often, higher uptake is noted in malignant tumors, while lower uptake more frequently signifies benign neoplasms. Soft tissue, bone, and cartilaginous tumors have all shown positivity [19]. Typical high-grade tumor features, such as central necrosis, can also be noted in ²⁰¹Tl-Chloride imaging; this finding is predictive of decreased survival [20].

¹⁸F-Fluoride is increasingly being used as a sensitive bone scanning agent for metastatic surveys for many cancers. This is also the case for sarcomas; however, the use of ¹⁸F-fluoride may extend beyond the detection of metastases in bone sarcomas. Since the hallmark of these tumors is new bone formation, uptake and distribution levels of ¹⁸F-Fluoride will likely change in response to therapy. A particular use may be in evaluating activity in lung metastases since it is common practice to resect lung metastases when they are quiescent after successful chemotherapy. Figure 23.3 shows a whole body ¹⁸F-fluoride bone scan.

Positron emission tomography (PET) with [¹⁸F]fluorodeoxyglucose ([¹⁸F]FDG) has been evaluated for use in sarcoma imaging. Recently, this imaging procedure has been investigated in treatment response evaluation. Diagnosis through imaging in primary cancers has several critical aspects for patient treatment planning. It is used to determine the ­biologic behavior of the tumor, often determining if the tumor is benign or malignant; however, sarcomas include numerous tumors that do not fit well with either category because they are locally aggressive, yet rarely metastatic. The tumor histologic type determined from biopsy and imaging data is also helpful in determining tumor grade, which is the propensity of the tumor to behave aggressively. Several prospective and retrospective studies have described the utility of [¹⁸F]FDG PET in sarcoma diagnosis. In soft tissue sarcoma, this imaging can reliably distinguish low-grade from high-grade tumors [21–23]. There is less ability to discriminate benign from low-grade tumors or intermediate-grade types from either high-grade or low-grade processes. Low-grade tumors are often difficult to distinguish through histologic criteria as well. Additionally, special features and [¹⁸F]FDG uptake are related to specific histologic types. For example, the atypical lipomas and the low-grade liposarcomas may have very ­similar tissue features and biological behavior. They often result in repeated local recurrence; nevertheless, in a large mass, the [¹⁸F]FDG appearance can be significant for identifying small areas of high-grade differentiation, which can lead to much worse treatment outcome than the low-grade majority of the tumor mass composition. Figure 23.4 shows several [¹⁸F]FDG PET examples of primary sarcoma tumors.