Primary Bone Cancer

Etiology

Though primary bone cancer is most often idiopathic, risk factors also play a role in developing this cancer.

• Genetic factors are linked. Germline abnormalities in hereditary cancer predisposition syndromes have an increased risk of later developing bone cancer through the downregulation of tumor suppressor genes or upregulation of oncogenes. The TP53 tumor suppressor gene is often altered in Li-Fraumeni syndrome, putting patients at an increased risk of developing osteosarcoma. Similarly, a mutation in the Rb1 gene leading to hereditary retinoblastoma is linked to osteosarcoma. Werner and Rothmund-Thomson syndromes are also linked to an increased risk of developing osteosarcoma.

• Previous treatment for cancer with radiotherapy is linked to an increased risk of developing primary bone cancer in later life, particularly when exposed to ionizing radiation in childhood.

• Several benign conditions show the potential to progress to primary bone cancer. Paget disease of the bone is a condition characterized by a disorder of bone metabolism, particularly osteoclastic function. These patients are at an increased risk of developing osteosarcoma; however, it is a rare complication. Enchondromas and osteochondromas are benign cartilaginous neoplasms that can later develop into malignant chondrosarcoma.[2][3][4][5]

Epidemiology

Primary bone cancer remains uncommon, accounting for 0.2% of all malignancies and 5% of childhood malignancies. In the United States, an estimated 3600 new cases of primary bone cancer were diagnosed in 2020, with 1720 deaths, making up 0.3% of all cancer deaths. The National Cancer Institute data shows that chondrosarcoma (40%) is most prevalent in adults, followed by osteosarcoma (28%). In children and adolescents, osteosarcoma (56%) is the most common, with Ewing sarcoma (34%) second. Chordoma, undifferentiated pleomorphic sarcoma, adamantinoma, fibrosarcoma, and giant cell tumor of the bone are also types of primary bone cancer; however, they are fewer in number. Primary bone cancer has a male predominance, with a worldwide osteosarcoma male-to-female ratio of 1.43 to 1.[6][7]

Pathophysiology

Primary bone cancer is a malignant tumor of the connective tissue with mesenchymal origin. The World Health Organisation determined 6 categories: chondrogenic, osteogenic, notochordal, vascular, other malignant mesenchymal, and miscellaneous (including Ewing sarcoma). The pathophysiology varies considerably between groups and, in some cases, is poorly understood.[6]

Osteosarcoma is a highly malignant osteogenic tumor that can develop in any bone. The tumor tends to develop near the metaphysis of long bones in young patients. The most common sites are the distal femur, proximal tibia, and proximal humerus, with high bone turnover. In adults, the axial skeleton is more common, where previous irradiation or metabolic disease of the bone is often associated. Common genetic changes are not present to explain the growth of this tumor type; however, 70% of cases demonstrate some level of chromosomal abnormality. Alterations in p53, Rb1, and deoxyribonucleic acid repair/surveillance genes are present in patients with Li-Fraumeni, Bloom, and Rothmund-Thomson syndrome, all linked to increased rates of osteosarcoma.[8][9][10]

Chondrosarcoma is primarily a disease of adults, most frequently diagnosed in patients between 30 and 60. They are generally slow-growing chondrogenic tumors of intermediate malignancy, rarely metastasizing. Chondrosarcoma arising de novo are classified as primary (>85% of cases), with those arising from pre-existing benign osteochondromas or enchondromas as secondary. The most common site for diagnosis is the long bones of the appendicular skeleton. Flat bones, including the pelvis, ribs, and scapula, can also be affected. The exact pathogenesis of chondrosarcoma is unknown, though multiple genes are implicated. Cytogenic studies have identified structural and numerical chromosomal abnormalities. Gene mutations in EXT1/2, TP53, Rb1, and IDH1/2 have also been linked to malignant transformation in benign lesions.[5][11]

Ewing sarcoma is an aggressive tumor of childhood and adolescence, most commonly occurring in the bone but also seen in soft tissues. The peak incidence is at 15 years, and the men-to-women ratio is 5:1. The most frequent sites involved are long bones in the lower limb, pelvic bones, and the axial skeleton (ribs and vertebral column). Ewing sarcoma develops characteristically at the diaphysis, in contrast to the pattern seen in osteosarcoma. Ewing sarcoma is genetically well described, with characteristic chromosomal translocations identified. The translocation leads to fusing an FET protein to an ETS transcription factor, most commonly FLI1 (>85% of cases). The result is the formation of fusion proteins that deregulate downstream genes, altering cell behavior.[12][13][14]

Histopathology

Diagnosis of primary bone cancer requires a tissue biopsy to perform histopathological assessment, with significant heterogeneity seen.

Osteosarcoma

The formation of bone or osteoid characterizes osteosarcoma, and this identification is key to diagnosis. Several histological subtypes have been identified, determined by the tumor's bone location and grade.[15][8]

Intramedullary:

• Conventional
• Most prevalent subtype, comprising 80% of all osteosarcomas
• Classically high-grade, arising from the intramedullary canal
• Spindle to polyhedral cell shape malignant mesenchymal cells are seen
• Cell nuclei are pleomorphic with occasional mitotic figures
• Extracellular matrix production can be osteoblastic, osteoclastic, or fibroblastic; a combination is common
• Telangiectatic
•  <4% of osteosarcomas
•  Dilated hemorrhagic sinusoids seen with small amounts of osteoid 
• Cavities mimic the appearance of an aneurysmal bone cyst, with the presence of high-grade sarcoma cells distinguishing the tumor
• Low-grade
• <2% of osteosarcomas
• Well-differentiated cells embedded in the osseous matrix and fibrous stroma, with small amounts of osteoid
• Small cell
• 1.5% of osteosarcomas
• Numerous small round malignant cells seen within an osteoid matrix. 
• Small cell sarcoma can resemble Ewing sarcoma; production of osteoid and sporadic spindling of cells are distinguishing features [15][8]

Surface:

• Parosteal 
• 1% to 6% of osteosarcomas
• Slow growing, arising from the outer surface of the metaphysis 
• Low-grade, with a well-differentiated, mostly cartilaginous matrix with minimal osteoid
• Periosteal
• 1% to 2% of osteosarcomas 
• More aggressive than parosteal osteosarcoma, with intermediate-grade tumors showing increased cell atypia 
• Mostly cartilaginous matrix with minimal osteoid
• High-grade
•  <1% of osteosarcomas 
• Histologically similar to conventional osteosarcoma, showing high-grade spindle-shaped cells with nuclear pleomorphism [15][8]

Chondrosarcoma

The production of hyaline cartilage characterizes chondrosarcomas to form a cartilaginous matrix. Lobules of cartilage are seen with significant variation in dimension. Cell nuclei show pleomorphism with chondrocytes varying in size and shape. Conventional chondrosarcoma accounts for over 85% of all chondrosarcomas. Chondrosarcoma can be subcategorized into primary central (developing within the medullary canal) or secondary peripheral (developing from the surface of the bone secondary to pre-existing enchondroma or osteochondroma). Histologically, both primary central and secondary peripheral are alike. Grading is an essential process that allows for the prediction of clinical behavior.[5][16][17]

• Grade I: These are low-grade, lowly cellular lesions with a predominantly cartilaginous matrix and small, dense nuclei. Distinguishing grade I chondrosarcoma and benign enchondroma can be difficult, both radiologically and histologically.
• Grade II: This shows a reduced cartilaginous matrix and moderately cellular. Nuclei are enlarged and hyperchromatic, with increased atypia. Mitoses may be seen.
• Grade III: These are high-grade lesions that are highly cellular, with increased cellular atypia showing vesicular and enlarged nuclei. Cartilaginous matrix is rare or absent, with myxoid material evident, and mitoses are more readily identified.

Several rare subtypes of chondrosarcoma are also identified. De-differentiated chondrosarcoma is characterized by low-grade chondrosarcoma next to a de-differentiated high-grade lesion, with a sharp transition between the 2. The tumor is extremely aggressive. Mesenchymal chondrosarcoma is a high-grade tumor occurring in either bone or soft tissue. Undifferentiated small round cells are seen with varying amounts of a cartilaginous matrix. Clear cell chondrosarcoma is a low-grade tumor, with cells showing clear, vacuolated cytoplasm. Areas of hemorrhage and cyst formation are seen.[5]

Ewing Sarcoma

Ewing sarcoma is a high-grade aggressive sarcoma and belongs to the group of small round-cell tumors. Monomorphic small cells are seen in sheets, with round nuclei, finely dispersed chromatin, and nucleoli usually unidentifiable. Frequently, necrosis is seen, with remaining viable cells arranged perivascularly. Cell membranes express the glycoprotein CD99, with immunohistochemistry showing that >95% of Ewing sarcomas have extensive membranous expression. CD99 expression is not specific to Ewing sarcoma; other markers are also used for diagnosis.[18][14]

Other Types of Primary Bone Cancer

Chordoma, adamantinoma, and giant cell tumors of bone are typically low-grade locally invasive tumors. Undifferentiated pleomorphic sarcoma and fibrosarcoma are aggressive malignant tumors with a generally poor prognosis.[19][20]

History and Physical

Primary bone cancer is a rare diagnosis, with primary care clinicians unlikely to encounter a single case. Early diagnosis improves overall survival; however, delays remain common. History and examination form the first steps in diagnosing primary bone cancer, and an urgent referral to a specialist center is needed for all patients with a possible diagnosis.[12][6]

Pain is the most common symptom, described as deep-seated dull pain progressing over time, refractory to simple analgesia. Pain can be troublesome at night, which is always a red flag. A mass may be palpable with localized tenderness. Patients may exhibit signs of systemic disease, including lethargy, malaise, and fever; however, in high-grade tumors, these are often not present and may suggest metastatic disease. A pathological fracture can be the first sign; any abnormal fracture requires further investigation. History of predisposing genetic conditions (eg, Li-Fraumeni syndrome, hereditary retinoblastoma, Werner syndrome, and Rothmund-Thomson syndrome) or diseases (Paget disease) is crucial.[6] Physical examination should focus on pain, tenderness, or mass. The site should be inspected and palpated, with size, consistency, mobility, location of the mass, and overlying skin changes noted. Lymph nodes should be palpated.[21]

Evaluation

Diagnostic modalities used in primary bone cancer include imaging, laboratory blood tests, and tissue biopsy.

Plain Film Radiograph

All patients should have orthogonal plain film radiographs when identifying potential bone cancer. Plain x-rays may show the following findings:

• Osteolytic, osteoblastic, or mixed changes
• A moth-eaten appearance (suggests bone destruction secondary to a rapidly expanding tumor within a bone, commonly seen in Ewing sarcoma and telangiectatic osteosarcoma)
• A permeative appearance (suggests the tumor progresses through bone, with an ill-defined zone between the tumor and healthy bone, often seen in small cell tumors, including Ewing sarcoma)
• "Onion skinning," with the tumor lifting partially-formed periosteal bone (classically seen in Ewing sarcoma)
• "Codman triangle," with periosteum lifted off bone and osteoid laid down
• "Sunburst" appearance, with vertical osteoid calcification due to significant periostitis [22]

Magnetic Resonance Imaging 

A magnetic resonance imaging, MRI, scan remains the gold standard for assessing local tumor extent. The whole anatomical compartment should be imaged, and the MRI should be sensitive for bone and soft tissue lesions. Biopsy planning is crucial, and MRI allows the definition of neurovascular structures. Modern techniques, including dynamic MRI, better characterize high-grade tumor areas and have been used to assess tumor response to chemotherapy.[6][23]

Computed Tomography 

A computed tomography, CT, scan is used when the diagnosis remains unclear following an MRI or if an MRI is contraindicated. CT remains the modality of choice in pelvic bone cancer and reconstructive surgery. Patients with confirmed primary bone cancer require staging, and although many centers still perform chest radiographs, a chest CT scan is the gold standard for assessing metastatic pulmonary disease.[6]

Whole-Body Bone Scintigraphy 

A whole-body bone scintigraphy bone scan is a nuclear medicine study that utilizes technetium-99m as an active agent, highlighting areas of osteoblastic activity. It allows the detection of malignancy and is useful in diagnosing metastatic disease.

Positron Emission Tomography 

The positron emission tomography, PET, scan is a nuclear medicine study that utilizes the high metabolic rate of tumor cells, measuring the uptake of injected radiolabeled F-18 fluoro-deoxy-glucose. A PET scan is in some centers for the initial staging of primary bone cancer, and studies have suggested it as a modality for follow-up when used in combination with a CT scan.[24]

Laboratory Blood Tests

Specific laboratory blood tests are not used in diagnosing primary bone cancer; however, they form part of the patient workup. In patients treated with chemotherapy, baseline urea, creatinine, and liver function tests allow baseline renal and hepatic function assessment. Biochemical markers alkaline phosphatase and lactate dehydrogenase offer some predictive value, and levels can be monitored in follow-up to assess for disease recurrence.[22]

Tissue Biopsy

A lesion biopsy is needed for definitive diagnosis, allowing for histopathological assessment and tumor grading. Biopsy should be performed with the operating surgical team, ideally in a specialist bone cancer center. The procedure requires meticulous planning, with suboptimal biopsy impacting definitive surgical treatment options. Imaging should be performed before a biopsy, aiding in approach planning and preventing tissue disruption that could make radiological assessment more difficult. Percutaneous, incisional, or excisional techniques are used. Ultrasound, x-ray, and CT scans allow precise guidance. The tract should be well marked, allowing for excision during surgery, and a specialist bone cancer pathologist should assess samples. Specific markers on immunohistochemistry staining would assist in the diagnosis. Greater than 95% of Ewing sarcomas show extensive membranous expression of CD99; this is not specific to Ewing sarcoma, so other markers are also used in the immunohistochemistry panel.[21]

Treatment / Management

Managing primary bone cancer requires a multidisciplinary approach by a specialist bone cancer center, including staff trained in providing age-appropriate care to children or adolescents. Management depends on several factors, including tumor type, stage and grade, and patient preference. Surgical excision remains the cornerstone of primary bone cancer treatment. Neoadjuvant and adjuvant chemotherapy are also commonplace in the management, with radiotherapy used in specific cases.

Surgery

Surgical resection aims to remove all tumor tissue with adequate margins while preserving as much limb function as possible. A decision for either limb salvage surgery or amputation is established using imaging, histopathology, response to adjuvant treatment, and patient wishes. Surgery often leads to significant tissue loss, and open discussion with the patient is vital. The surgery's potential risks, benefits, and expected long-term functional impact must be highlighted. Low-grade tumors amenable to surgical excision typically require wide excision (removing the involved part of the bone with a cuff of healthy tissue), with high-grade tumors requiring radical excision (removing the affected bone and associated soft tissues within the anatomical compartment).[6][25]

Chemotherapy

Multiple chemotherapy agents and regimens are used to manage primary bone cancer. Often, this consists of induction (neoadjuvant) and postoperative combination therapy (adjuvant), with improvements in rates of limb salvage surgery and overall survival since their introduction. Chemotherapy forms part of the standard treatment protocol for osteosarcoma and Ewing sarcoma. Chondrosarcoma is still primarily managed surgically, except in cases of mesenchymal chondrosarcoma, where chemotherapy and radiotherapy are often used.[26][27](B3)

Neoadjuvant chemotherapy is primarily used to reduce the rate of future metastatic spread; however, study results have suggested it can also contribute to primary tumor control. A good response to neoadjuvant therapy is determined by a histological necrosis rate of less than 90%, with a poor response indicating a change in postoperative adjuvant chemotherapy agents and poorer outcomes.[28][29][30](A1)

Radiotherapy

Radiotherapy is often used as adjunctive therapy in primary bone cancer. Ewing sarcoma is a radiosensitive tumor, with radiotherapy commonly used as part of the definitive treatment plan. Preoperative radiotherapy is used if the response to neoadjuvant chemotherapy is poor or the tumor is positioned in a problematic anatomical location, where reduction of tumor volume will aid surgical resection. If sufficient tumor volume cannot be removed surgically or it would be unacceptably disabling, radiotherapy is used for local treatment. Where adequate margins have not been resected, postoperative radiotherapy is utilized. Chondrosarcomas are relatively radioresistant, with radiotherapy only utilized for surgically unresectable or incompletely resected tumors. Radiotherapy has a palliative role in all primary bone cancers and is used to slow tumor growth locally and relieve pain.[6][31][32](B2)

Differential Diagnosis

The differential diagnosis of primary bone cancer includes the following:

Malignant Types of Tumors

• Metastases
• Lymphoma
• Multiple myeloma

Benign Types of Tumors

• Giant cell tumor
• Osteoblastoma
• Enchondroma
• Chondromyxoid fibroma
• Cortical desmoid

Infection

• Osteomyelitis

Trauma

• Fracture callus

Other

• Aneurysmal bone cyst
• Fibrous dysplasia [33]

Staging

Two staging systems, the TNM and Enneking systems, are used in primary bone cancer.

TNM System, American Joint Committee on Cancer 

This refers to the extent of tumor (T), spread to local lymph nodes (N), metastatic spread (M), and histological grade (G).[34]

Stage IA (T1 N0 M0 G1/GX)

•  ≤8cm in size, with no lymph node or metastatic spread
• Low grade

Stage IB (T2 N0 M0 G1/GX, or T3 N0 M0 G1/GX)

• >8cm in size (T2), with no lymph node or metastatic spread; low grade
• Cancer at more than 1 location in the same bone (T3), with no lymph node or metastatic spread; low grade

Stage IIA (T1 N0 M0 G2/G3)

• ≤8cm in size, with no lymph node or metastatic spread; high grade

Stage IIB (T2 N0 M0 G2/G3)

• >8cm in size, with no lymph node or metastatic spread; high grade

Stage III (T3 N0 M0 G2/G3)

• Cancer at more than 1 location in the same bone, with no lymph node or metastatic spread; high grade

Stage IVA (Any T N0 M1a Any G)

• Any size and maybe in multiple locations in the same bone, with no lymph node involvement. 
• Metastatic spread to the lungs (M1a); any grade

Stage IVB (Any T, N1, Any M, Any G, or Any T, Any N, M1b, Any G)

• Any size; may be in more than 1 location in the same bone 
• Has spread to local lymph nodes (N1)
• May or may not have metastasized to distant organs; any grade
• Any size and maybe in more than 1 location in the same bone. 
• May or may not have spread to local lymph nodes 
• Metastatic spreads to distant sites like other bones, liver, or brain (M1b); any grade

Enneking System

Refers to the histological grade (G), the extent of the tumor to the anatomical compartments of the body (T), and metastatic spread (M).[35]

Stage IA (G1 T1 M0)

• Low grade, intra-compartmental, no metastasis

Stage IB (G1 T2 M0)

• Low grade, extra compartmental, no metastasis

Stage IIA (G2 T1 M0)

• High grade, intra-compartmental, no metastasis

Stage IIB (G2 T2 M0)

• High grade, extra compartmental, no metastasis

Stage III (Any G, Any T, M1)

• Any grade, any location, regional, or distant metastatic spread

Prognosis

The prognosis of primary bone cancer is dependent on multiple factors, and no significant improvement is seen in 5-year survival over the past 25 years. In the United States, the National Cancer Institute shows that the overall 5-year survival rate is 66%, with studies suggesting lower rates in the United Kingdom.[12]

When the disease is localized, osteosarcoma has a 10-year survival of 60% to 78%. This number falls to 20% to 30% in patients with metastatic disease at presentation, with other negative prognostic factors including axial or proximal extremity tumor location, increased tumor size, raised alkaline phosphatase or lactase dehydrogenase, increased age, pathological fracture, and poor response to neoadjuvant chemotherapy.[36][37][38]

The most potent prognostic factor in chondrosarcoma is histological grade. Other identified factors are metastatic disease at presentation, increased age, and pelvic tumor location. 5-year survival in grade I chondrosarcoma is 83%, with only 53% of patients surviving to 5 years with grade I and II diseases.[5][39][40] Ewing sarcoma has a 5-year survival of 70% to 80% when the disease is localized. This number falls to 50% in patients with isolated pulmonary metastases and less than 30% in patients with any other metastatic disease at diagnosis. Other negative prognostic factors include pelvic tumor location, increased tumor size, and poor response to neoadjuvant or adjuvant chemotherapy treatment.[14][41]

Complications

The complications of primary bone cancer include the following:

Tumor-Related Complications

• Pathological fracture
• Tumor recurrence
• Distant metastasis [42][27]

Treatment-Related Complications

• Surgery
  • Surgical site or periprosthetic infection
  • Implant failure
  • Non-union/fracture of the biological implant
• Chemotherapy
  • Short-term side effects include malaise, anemia, nausea, vomiting, and alopecia
  • Long-term side effects include cardiotoxicity, renal toxicity, hearing loss, and an increased risk of secondary malignancy
• Radiotherapy
  • Side effects following radiation therapy are site-dependent, affecting the skin, pelvic organs, gastrointestinal tract, and lungs
  • Long-term, a small increased risk of developing a secondary malignancy exists [43][44][45]