Bone Tumors and Soft Tissue Sarcomas

Non-modifiable — germline cancer predisposition

• **Li-Fraumeni syndrome (germline TP53)**: loss of the guardian of the genome permits accumulation of the complex karyotypic damage typical of osteosarcoma; suspect when a child with osteosarcoma has relatives with breast cancer, adrenocortical carcinoma, or brain tumors
• **Hereditary retinoblastoma (germline RB1)**: survivors carry a lifelong risk of osteosarcoma, amplified further in previously irradiated fields — the classic "second malignancy" stem
• **Hereditary multiple exostoses (*EXT1*/*EXT2*)**: multiple osteochondromas from defective heparan sulfate signaling at the physis; risk of secondary chondrosarcoma is higher than with a solitary osteochondroma
• **Enchondromatosis (Ollier disease, Maffucci syndrome)**: *IDH1/IDH2*-mutant cartilage rests undergo malignant transformation to chondrosarcoma; Maffucci adds soft tissue hemangiomas
• Neurofibromatosis type 1: plexiform neurofibromas may transform into malignant peripheral nerve sheath tumor
• DICER1 and Beckwith-Wiedemann syndromes: predispose to embryonal rhabdomyosarcoma

Non-modifiable — host and demographic factors

• Rapid skeletal growth: osteosarcoma clusters at the metaphyses of the fastest-growing bones during the pubertal growth spurt, and affected children are often taller than peers; slight male predominance
• Ancestry: Ewing sarcoma is distinctly uncommon in patients of African or Asian ancestry, a frequently tested epidemiologic clue
• Paget disease of bone: high-turnover pagetic bone in an older adult can give rise to secondary osteosarcoma — signaled by new pain or a lytic destructive change in a known pagetic bone
• Prior benign lesion: chondrosarcoma may arise within a preexisting enchondroma or the cartilage cap of an osteochondroma

Modifiable / acquired exposures

• Therapeutic ionizing radiation: latency of years to decades; NCCN Bone Cancer guidance treats prior radiation as a defining risk for radiation-associated sarcoma within the treated field
• Alkylating agents and topoisomerase II inhibitors: cyclophosphamide, ifosfamide, and etoposide raise the risk of secondary bone sarcoma and secondary leukemia
• Chronic lymphedema: post-mastectomy or filarial lymphedema predisposes to lymphangiosarcoma (Stewart-Treves syndrome)
• Chemical exposures: vinyl chloride, arsenic, and thorotrast are linked to hepatic angiosarcoma

• Distractor to reject: trauma does not cause sarcoma; an injury merely draws attention to a preexisting mass.

BONE TUMORS

• Osteosarcoma: Arises from osteoblasts with uncontrolled proliferation and abnormal bone matrix production; associated with TP53 mutations (Li-Fraumeni syndrome), RB1 mutations, and increased risk after radiation therapy; typically high-grade with early metastatic potential (20% have pulmonary metastases at diagnosis)

• Ewing sarcoma: Results from t(11;22) translocation producing EWSR1-FLI1 fusion oncogene; arises from primitive neuroectodermal cells in bone marrow; characterized by small blue cells with high mitotic activity and necrosis; aggressive behavior with early hematogenous spread (25% have metastases at presentation)

• Chondrosarcoma: Malignant transformation of hyaline cartilage with mutations in IDH1, IDH2, and CDKN2A; typically lower-grade than osteosarcoma but more chemoresistant; often arises from preexisting benign lesions (enchondroma, osteochondroma)

• Giant cell tumor of bone: Contains neoplastic stromal cells with H3F3A mutations producing RANKL, which recruits osteoclast-like multinucleated giant cells; benign but locally aggressive with recurrence potential

SOFT TISSUE SARCOMAS

• Rhabdomyosarcoma: Arises from embryonal mesenchyme with PAX3-FOXO1 or PAX7-FOXO1 fusions (alveolar type); most common soft tissue sarcoma in children; skeletal muscle origin with aggressive behavior

• Liposarcoma: Malignant transformation of lipocytes with FUS-DDIT3 or EWSR1-DDIT3 fusions (myxoid type) or MDM2/CDK4 amplification (well-differentiated/dedifferentiated types)

• General sarcoma mechanisms: Chromosomal translocations producing fusion oncoproteins, loss of tumor suppressors (TP53, RB1), activation of growth signaling pathways (KIT, PDGFRA), and angiogenesis promoting rapid growth in permissive soft tissue environment

BONE TUMORS

• Localized pain and swelling: Most common presenting symptom; often insidious onset progressing over weeks to months; osteosarcoma typically around the knee (distal femur, proximal tibia) in adolescents; Ewing sarcoma more diaphyseal distribution in femur and pelvis

• Palpable mass: Often firm, warm, and tender; may restrict joint motion or cause limp; soft tissue component visible on exam in advanced cases

• Systemic symptoms: Constitutional symptoms (fever, weight loss, malaise) more common in Ewing sarcoma than osteosarcoma; reflects high tumor burden and inflammatory response

• Pathologic fracture: Occurs through weakened bone; may be presenting event; indicates advanced local disease

• Age-related presentation: Osteosarcoma peaks at ages 10-25 (growth spurts); Ewing sarcoma ages 10-20; chondrosarcoma typically older patients (>40 years); giant cell tumor ages 20-40

SOFT TISSUE SARCOMAS

• Painless mass: Progressive enlargement over weeks to months; often deep-seated and initially subclinical; superficial sarcomas present earlier due to visible swelling

• Functional impairment: Depending on location—nerve or vessel compression causing weakness, paresthesias, or edema; bowel/bladder dysfunction if intra-abdominal

• Constitutional symptoms: More prominent in advanced or high-grade tumors; indicates systemic involvement or metabolic derangement

• Rhabdomyosarcoma specifics: Often presents as mass in orbit (proptosis, vision changes), biliary tract (jaundice), bladder (hematuria), or extremities; more common in children <5 years

• Imaging - Plain radiographs: Assess bone involvement, cortical destruction, periosteal reaction; Codman triangle and sunburst pattern suggest osteosarcoma (aggressive periosteal new bone); "onion skin" periosteal reaction suggests Ewing sarcoma; "popcorn" calcifications suggest chondrosarcoma

• Advanced imaging (MRI primary for soft tissue; CT for bone staging): MRI best for soft tissue extent, marrow involvement, and neurovascular assessment; CT chest mandatory for pulmonary metastatic staging (most common site); PET/CT for skeletal metastases and treatment response

• Tissue diagnosis - Needle or open biopsy: Core needle biopsy preferred for most lesions (less contamination than excisional biopsy); biopsy tract orientation critical as entire tract must be excised with tumor; fine needle aspiration insufficient for diagnosis

• Histopathology with immunohistochemistry: Osteosarcoma shows malignant cells producing osteoid/bone; Ewing sarcoma shows FLI1 and CD99 positivity; rhabdomyosarcoma shows desmin and myogenin positivity; liposarcoma shows MDM2 and CDK4 amplification on FISH

• Molecular testing: Fluorescence in situ hybridization (FISH) for characteristic translocations; increasingly important for prognosis and targeted therapy eligibility; PAX3/PAX7-FOXO1 status predicts rhabdomyosarcoma aggressiveness

• Laboratory studies: Alkaline phosphatase and LDH elevated in osteosarcoma (prognostic significance); CBC for baseline; renal and hepatic function before chemotherapy; consider tumor markers specific to histology

• Grading systems: Enneking surgical staging for bone tumors (stage based on grade, intraosseous/extraosseous, and metastases); AJCC TNM for soft tissue sarcomas (grade, size, depth, location); Grade critical for prognosis and treatment intensity

OSTEOSARCOMA

• Chemotherapy first-line: Neoadjuvant chemotherapy (3 months before surgery): cisplatin, doxorubicin, and methotrexate (MAP regimen); allows tumor response assessment and micrometastatic treatment; improves 5-year survival to ~70% when combined with surgery

• Surgical resection: Wide excision with negative margins (typically 2-3 cm margins); limb-salvage surgery preferred when feasible (reconstruct with prosthetic, allograft, or autograft); amputation if neurovascular involvement or inadequate margins achievable; timing typically 10-12 weeks after starting chemotherapy

• Adjuvant chemotherapy: Continued for 6-9 months total; dose intensity important for prognosis; poor responders to neoadjuvant (>90% necrosis remains favorable) may benefit from intensified regimens

• Metastatic disease: Resection of pulmonary metastases improves survival; consider for isolated lesions; newer agents (sorafenib, pazopanib) showing promise in recurrent/refractory disease

EWING SARCOMA

• Multimodal therapy essential: Chemotherapy + surgery + radiation for best outcomes; 5-year survival improved from 10% (chemotherapy alone era) to ~70% with current approaches

• Neoadjuvant chemotherapy: VDC/IE regimen (vincristine/doxorubicin/cyclophosphamide alternating with ifosfamide/etoposide) for 10-14 weeks; response assessment critical for prognosis

Disease-related

• Pulmonary metastasis: hematogenous spread through thin-walled marrow sinusoids seeds lung first in both osteosarcoma and Ewing sarcoma; new nodules on surveillance chest CT, or dyspnea/hemoptysis, signal it — resection of isolated pulmonary metastases is still potentially curative per NCCN Bone Cancer guidance
• Pathologic fracture: cortical destruction plus tumor osteoid that lacks normal lamellar architecture; abrupt pain and deformity after trivial load. Impending fracture of a weight-bearing bone is a surgical urgency, and the fracture hematoma can contaminate compartments and jeopardize limb salvage
• Epidural extension with spinal cord compression: pelvic and vertebral Ewing sarcoma; back pain with saddle anesthesia, weakness, or sphincter loss is an emergency — urgent MRI, corticosteroids, and neurosurgical/radiation oncology involvement
• Local recurrence from biopsy tract seeding: an ill-planned or transversely oriented biopsy contaminates tissue planes and can convert a limb-salvage candidate into an amputation

Treatment-related

• Anthracycline cardiomyopathy: doxorubicin-induced topoisomerase IIβ inhibition and oxidative injury cause cumulative dose-dependent LV dysfunction; detected by falling LVEF or global longitudinal strain on serial echocardiography, as advised in the Children's Oncology Group long-term follow-up guidelines. Overt decompensated heart failure is an emergency
• Cisplatin toxicity: proximal tubular injury with magnesium wasting, irreversible high-frequency sensorineural hearing loss (audiometry before each cycle), and stocking-glove neuropathy
• High-dose methotrexate toxicity: crystalline tubular precipitation with delayed clearance causes mucositis, myelosuppression, and acute kidney injury — prevented by alkalinization, hydration, and leucovorin rescue, with glucarpidase for severely delayed clearance
• Ifosfamide/cyclophosphamide: acrolein-mediated hemorrhagic cystitis (gross hematuria; prevented with mesna and hydration) and ifosfamide encephalopathy
• Febrile neutropenia: an emergency — blood cultures and empiric antipseudomonal beta-lactam within an hour, per IDSA/ASCO neutropenic fever guidance
• Tumor lysis syndrome: bulky, chemosensitive Ewing sarcoma; hyperkalemia, hyperphosphatemia, hyperuricemia, hypocalcemia with acute kidney injury — an emergency
• Late effects: secondary leukemia (alkylators, etoposide), radiation-associated sarcoma, limb-length discrepancy and prosthetic loosening or infection after limb salvage, and osteonecrosis of the jaw or rebound hypercalcemia after denosumab for giant cell tumor.

• Radiographic buzzwords map to a diagnosis, not a treatment: Codman triangle and sunburst metaphyseal lesion around the knee in a teenager = osteosarcoma; onion-skin periosteal reaction in a diaphysis = Ewing sarcoma; popcorn or rings-and-arcs calcification in an adult pelvis/proximal femur = chondrosarcoma; soap-bubble lytic epiphyseal lesion in a 20–40-year-old = giant cell tumor.
• Ewing sarcoma mimics osteomyelitis: fever, leukocytosis, elevated ESR/CRP, and a painful diaphyseal lesion. The single best next step is imaging plus biopsy, not empiric antibiotics alone — small round blue cells that are CD99 (MIC2) membrane-positive with t(11;22) seal it.
• The one association examiners love: hereditary retinoblastoma (RB1) survivors → osteosarcoma, with prior radiation multiplying the risk; Li-Fraumeni (TP53) is the other.
• Osteochondroma is the most common benign bone tumor — a cartilage-capped exostosis whose cortex and medullary cavity are continuous with the parent bone. Growth after skeletal maturity, new pain, or a thick cartilage cap on MRI suggests transformation to chondrosarcoma.
• Osteoid osteoma: night pain dramatically relieved by NSAIDs, with a small radiolucent nidus surrounded by reactive sclerosis; distinguish from osteoblastoma, which is larger, often in the posterior vertebral elements, and not NSAID-responsive.
• Best next step for any suspected primary bone or soft tissue sarcoma: MRI of the entire involved bone/compartment and referral to a sarcoma center for a planned core needle biopsy performed by the team that will resect it — NCCN emphasizes biopsy at the treating center because the tract must be excised en bloc. Chest CT completes staging.
• Distractor to avoid: excisional "shell-out" of an unstaged soft tissue mass (the whoops procedure) contaminates planes and worsens outcomes. Any soft tissue mass that is deep to fascia, enlarging, or larger than a golf ball deserves MRI first.
• Second distractor: in a patient over 40 with a lytic bone lesion, metastasis (breast, lung, thyroid, renal, prostate) or myeloma is far more likely than a primary bone sarcoma.