The GTM staging system is commonly used in staging of skeletal tumors in which the capital “G” indicates histological grade, “T” stands for local tumor extension, and “M” represents distant metastasis. The GTM staging system is used for both benign and malignant lesions (Tables 35.4A and 35.4B).

The local extension and metastatic spread of suspected malignant lesions should be evaluated before biopsy; radiological staging includes a chest CT and a whole body bone scan, in addition to MRI of the primary lesion. The entire length of the involved bone should be viewed by MRI to detect satellite lesions. Biopsy is the final diagnostic step in the evaluation of skeletal malignancies, and should be performed following radiological staging and multidisciplinary assessment (orthopedic oncology, radiology, pathology, medical oncology, radiation oncology). Biopsy material can be obtained by open or closed methods (e.g., fine needle aspiration, tru-cut, trochar). It is mandatory to ascertain the exact histopathological diagnosis of any suspected malignant lesion before deciding its definitive treatment. As a general rule, it is recommended that the biopsy should be performed by the surgeon who will perform the definitive surgery.

Definition and classification of surgical margins is beneficial in planning the treatment. Most skeletal tumors are surrounded by a reactive sclerotic rim. This reactive sclerotic rim is also surrounded by a reactive zone, which includes microscopic tumor invasion. Beyond the reactive zone lies the normal tissue. High-grade sarcomas may not include a reactive sclerotic rim, a feature that indicates the aggressiveness of the lesion. Based on surgical margins, four types of surgical resections are defined: intralesional, marginal, wide, and radical (Fig. 35.3). Intralesional (the tumor is removed by disrupting its capsule or pseudocapsule) and marginal resections (the tumor is removed by a margin that may include a contaminated reactive zone) may remain macroscopic and microscopic tumor residues, respectively. Wide resection, which includes reactive zone and non-contaminated surrounding tissues, is the gold standard at local control of malignant bone lesions. Functional loss is a common complication of radical resections, in which the whole compartment including the tumor is resected [4].

Osteoid osteoma constitutes 10–12 % of all benign skeletal tumors. Osteoid osteoma can be detected in any bone; however, it is most commonly observed in the femur and tibia. The most common presenting symptom is pain. Pain in osteoid osteoma is characteristic for not being relevant with motion, increasing especially during night-time and mostly relieved by aspirin and non-steroid anti-inflammatory drugs (NSAID). Lower extremity lesions may manifest with limping. Vertebral lesions may exhibit a nonstructural scoliosis.

Osteoblastoma is a rare bone-forming tumor, whose radiologic and histological properties resemble osteoid osteoma. This lesion is also known as “Giant Osteoid Osteoma.” The posterior vertebral arch is the predilection site for osteoblastomas, where more than 40 % of the cases arise. A progressively increasing pain not related with motion, is the most common finding. Limping may be the initial symptom in lower extremity involvement. Similarly vertebral involvement may primarily manifest as scoliosis. In plain radiographic views, lesions may present as lytic areas 2–10 cm in diameter. CT views may show intralesional calcifications (Fig. 35.5). Extended curettage and grafting is recommended for the treatment of this locally aggressive lesion. Larger lesions, vertebral and pelvic involvements, which are prone to intensive bleeding due to their rich vascularization may require selective arterial embolization prior to surgery. Risk of recurrence even after complete resection varies between 10 and 20 %.

Osteosarcoma is characterized by osteoid producing malignant cells. They constitute 20 % of primary malignant skeletal tumors, being the second most common following multiple myeloma. Ninety-five percent of the cases are at the second decade of life. Ninety-five percent of osteosarcomas diagnosed in children and young adults arise as primary tumors. Secondary osteosarcomas that arise over an existing bone lesion (e.g., fibrous dysplasia), an underlying bone disease (e.g., Paget) or previous radiotherapy, are rare malignancies that mostly occur during the seventh and eighth decades of life.

High-grade intramedullary osteosarcomas constitute 85 % of all osteosarcoma causes. They commonly involve metaphyses of long bones where the vascularization and growth potential is exceptional. Distal femoral and proximal tibial lesions, where most of the skeletal growth is processed, constitute 50–60 % of all conventional osteosarcoma cases. Proximal humerus, proximal femur, and pelvis are the other common locations, respectively. The main complaints in admission are progressive pain and localized swelling, which are ignored or remain misdiagnosed for several months. Approximately 15 % of newly diagnosed conventional osteosarcoma patients have accompanying pulmonary metastatic disease. The presence of clinically detectable metastatic disease is a strong predictor of poor prognosis [6].

The term “juxtacortical” refers to a group of osteosarcomas, which are originated from the surface of the bone, and composed of parosteal, periosteal, and high-grade surface osteosarcoma variants. They are commonly encountered in the third and fourth decades of life. Parosteal osteosarcomas are low-grade osteosarcomas, which commonly arise from posterior surface of distal femur. Periosteal osteosarcomas are mostly an intermediate-grade chondroblastic type osteosarcoma and, as their name implies, commonly involve more diaphyseal localizations than parosteal osteosarcomas. Parosteal and periosteal osteosarcoma subtypes are managed by wide resection, and since both lesions are low- and intermediate-grade, their metastatic potentials are lower when compared to conventional osteosarcomas. Inadequate surgical resections are related with local recurrence. High-grade surface osteosarcomas are the least common variant of this group, which resemble conventional osteosarcomas histopathologically. Local recurrences may progress to more aggressive and high-grade lesions. High-grade osteosarcomas, like conventional osteosarcomas, require chemotherapy and surgery.