Approach to Bone and Soft Tissue Tumors

Sarcomas are a heterogeneous group of rare mesenchymal malignant tumors. These tumors can arise in all sites of the body and are classified by their line of differentiation according to the type of mature tissue they resemble, either muscle, fat, fibrous tissue, bone, cartilage, blood vessels, or peripheral nerves. Benign mesenchymal tumors closely resemble normal tissue and have weak capability to invade local tissues, with little to no growth over time and typically do not recur after treatment. The incidence of benign tumors vastly outnumbers malignant tumors. Sarcomas, however, are locally aggressive and have the capacity to invade the surrounding soft tissues, with a destructive growth pattern. They may recur locally and also systemically in the form of metastatic disease.

There were approximately 13,000 new cases of soft tissue sarcomas (STS) and 3500 cases of bone/cartilage sarcomas diagnosed in the United States in 2019, accounting for <1% of all cancers; however, this is potentially an underestimate of the true incidence, with the annual incidence increasing over time as the population ages. Although STS account for <1% of all types of cancer, they accounted for nearly 7000 cancer-related deaths in 2019. Sarcomas can occur at all ages, though STS are more common in adults and bone sarcomas are more common in children and adolescents. Age can also be a predictive factor of the diagnosis for some patients with a sarcoma. Children are more likely to have a rhabdomyosarcoma, osteosarcoma, or Ewing sarcoma, while adults more commonly have an undifferentiated pleomorphic sarcoma (UPS), myxofibrosarcoma, chondrosarcoma, or liposarcoma. Sarcomas can occur anywhere in the body; however, tumors arising in the extremities account for a majority of cases, with the thigh being the most common site. Similar to age, certain sarcomas have a predilection for specific anatomic locations: epithelioid sarcoma and synovial sarcoma are common in the hands; osteosarcoma and Ewing sarcoma are common in the femur; while liposarcomas are common in the lower extremities and retroperitoneum.

Workup of a Bone or Soft Tissue Tumor

It is critical to perform an appropriate workup of a patient with a suspected sarcoma, which includes multidisciplinary management. In the process of examining a patient, the treating team needs to evaluate how invasive the tumor is using appropriate history, physical examination, and local imaging. Once this is completed, obtaining a tissue diagnosis (biopsy) is essential. Following diagnosis, the patient should be staged to evaluate for metastatic disease and be evaluated by a multidisciplinary care team.

History and Examination

A thorough history-taking and examination is key for all patients with a possible sarcoma ( Box 1.1 ). This can help the clinician formulate a treatment plan and determine what additional imaging modalities may be necessary to obtain a diagnosis. The rapid growth of a new mass or new rapid growth of an existing mass raises concern for a sarcoma. Some benign tumors are known to change in size with activity, in addition to becoming painful with the use of the extremity (vascular malformations and ganglion cysts). Fixed masses likely arise from or involve the underlying bone, and having the patient contract the muscle adjacent to the mass and assessing mobility can determine if it is adherent to the underlying fascia ( Box 1.2 ). Rarely, sarcomas can metastasize to lymph nodes, and certain subtypes (rhabdomyosarcoma, epithelioid sarcoma, clear cell sarcoma, and angiosarcoma) have a higher propensity for lymphatic spread. In those cases, the regional lymph node basin should be examined clinically and if there is a concern, evaluated with imaging.

Box 1.1

History of Patients with a Suspected Bone or Soft Tissue Sarcoma

PATIENT HISTORY	WHY IT IS IMPORTANT
Family history of cancer	Li-Fraumeni syndrome: Associated with bone and soft tissue sarcomas Multiple hereditary exostoses Associated with cartilage tumors (benign and malignant) Neurofibromatosis Associated with nerve sheath tumors (benign and malignant) Familial rhabdoid predisposition syndrome Rhabdoid tumors DICER syndrome: Embryonal rhabdomyosarcoma
Personal history of cancer	Consideration for metastatic disease Breast, renal. prostate, lung and thyroid carcinoma accounts for a majority of bony metastatic disease Children with a history of neuroblastoma can develop metastatic disease to bone
Patient age	Children and adolescents: Osteosarcoma, Ewing sarcoma, rhabdomyosarcoma Adults: Metastatic disease, myeloma, lymphoma, soft tissue sarcomas, chondrosarcoma
Exposure	Radiation Radiation associated sarcomas Pesticides/herbicides Soft tissue sarcomas Vinyl chloride Hepatic angiosarcoma
Growth	Slow growing over time Likely benign, however deep or pelvic masses are often difficult to fully ascertain how long they have been growing Rapidly growing new mass or change in growth velocity Concern for sarcoma
Pain pattern	Incidentally found painless bony mass Likely benign Night pain Requires narcotics–concerning for malignant tumor Relieved by aspirin/nonsteroidal anti-inflammatories – osteoid osteoma
History of recent injury	Typically not associated with a sarcoma Potential for healing fracture or an underlying infection
Systemic symptoms	Concerning for a malignancy or infection Benign tumors typically do not cause fevers, chills, weight loss or fatigue In children: may be with angiomatoid fibrous histiocytoma and inflammatory myofibroblastic tumor
Previous arthroplasty	Pseudotumor

Box 1.2

Physical Exam Findings in Patients with a Suspected Sarcoma

EXAM FINDINGS	WHY IT IS IMPORTANT
General appearance	Ill-appearing: Consideration for infection, hematological malignancy, metastatic disease
Skin color/swelling/pain	Erythema/swelling/pain Aggressive process Consideration for infection Evaluate skin for stigmata of other disease processes Birth marks, neurofibromas, telangiectasia
Location	Soft tissue Superficial or deep Bone: Diaphysis – Ewing sarcoma Metaphysis – osteosarcoma, chondrosarcoma, giant cell tumor
Mobility	Range of motion of the joints above and below mass should be evaluated Determine if the mass is “fixed” or “mobile” with range of motion of joints
Size	Tumors larger than a golf ball (>4 cm) are concerning for a malignant process
Consistency of mass	Soft, rubbery masses Likely benign Firm masses Concerning for malignant tumor
Enlarged lymph nodes	Potential metastatic sarcoma based on histology Epithelioid sarcoma, clear cell sarcoma, rhabdomyosarcoma, angiosarcoma, Ewing sarcoma Hematological malignancy Infection

Local Imaging

Sarcomas are known for a centripetal growth pattern along tissue planes leading to compression of the surrounding tissues; however, they often do not violate fixed anatomic barriers. Initial evaluation of sarcomas often involves plain film radiographs and magnetic resonance imaging (MRI).

Plain Radiographs

Plain radiographs should be the initial imaging of choice for all patients with a suspected bone or soft tissue mass. Large masses can obscure the normal fat planes by distorting the interface between the muscle and fat. In addition, radiographs can identify bone invasion and remodeling, as well as soft tissue calcification or ossification. Initial radiographs should be performed with anterior-posterior projections in addition to orthogonal views of the affected area. When a mass is detected on plain radiographs, the tumor should be categorized by its location and whether it has either benign (nonaggressive) or malignant (aggressive) features ( Fig. 1.1 ). Types of bone destruction are categorized as purely lytic, purely sclerotic, and mixed lytic and sclerotic.

It is important to evaluate the bone destruction in terms of what the tumor is doing to the bone , and what the bone is doing to the tumor . This can help determine if the tumor is aggressive or nonaggressive. The margin formed between lytic lesions and the adjacent host bone infers how aggressive the tumor is. Typically tumors with a slow pattern of growth will have a “geographic” or narrow zone of transition between host bone (i.e., one can draw a line around the tumor), while tumors with indistinct margins (wide zone of transition), which can be defined as “moth-eaten” or “permeative,” are associated with aggressive tumors. The reaction of the periosteum indicates the host bone response to how fast the tumor is growing. Aggressive patterns of reaction (hair-on-end or sunburst) and elevation of the periosteum (Codman triangle) are associated with malignant tumors. Benign features include solid or unilamellar reactive bone formation around the tumor.

The location of the tumor ( Table 1.1 ), in addition to the matrix mineralization patterns, can help narrow the differential. Malignant tumors such as an osteosarcoma or chondrosarcoma are commonly found in the metaphysis, while round blue cell tumors (Ewing sarcoma, lymphoma, and myeloma) are common in the diaphysis; although can be seen in the metaphysis as well. Purely epiphyseal or apophyseal tumors (chondroblastoma or infection) are commonly benign. The presence of either chondroid (stippled, comma, or pop-corn shaped) or osteoid (fluffy and ill-defined calcification) matrix can be an indicator of the type of tumor present, but matrix formation can be found in benign and malignant lesions. In addition, some soft tissue masses (synovial sarcoma, vascular malformations, and myositis ossificans) are known to have soft tissue calcifications.

Table 1.1

Common Location for Tumors Based on Location in Bone

Diaphysis	Metaphysis (Central)	Metaphysis (Eccentric)	Epiphysis/Apophysis
Metastatic Disease	Osteomyelitis	Osteomyelitis	Osteomyelitis
Myeloma	Chondrosarcoma	Giant Cell Tumor	Chondroblastoma
Lymphoma	Enchondroma	Osteosarcoma	Clear Cell Chondrosarcoma
Ewing Sarcoma	Unicameral (Solitary) Bone Cyst	Chondrosarcoma	Synovial Cyst
Osteoid Osteoma (Cortical Lesion)	Chondromyxofibroma	Aneurysmal Bone Cyst	Dysplasia Epiphysealis Hemimelica (Trevor Disease)
Adamantinoma	Metastatic Disease	Nonossifying Fibroma	Giant Cell Tumor
Fibrous Dysplasia	Myeloma	Osteochondroma
Osteofibrous Dysplasia

Computed Tomography

Computed tomography (CT) serves as an extension of radiographic evaluation and can better define periosteal reaction, the margin of a tumor, and matrix formation. Image-guided biopsy is often performed with CT as it allows for planning a safe approach and captures the path of the needle. For small, cortically based tumors such as an osteoid osteoma, CT is the imaging of choice for diagnosis ( Fig. 1.2 ). In addition, CT is used to stage patients for metastatic disease and can be used to provide cross-sectional imaging in patients with contraindications to MRI.

Fig. 1.2, The utility of a CT scan to diagnosis an osteoid osteoma. Initially, the radiographs showed thickening of the cortical bone of the proximal femur (A). A CT scan showed a central nidus (B) consistent with an osteoid osteoma, which was subsequently treated with a CT-guided radiofrequency ablation (C).

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