A 62-year-old retired professor comes to the clinic with the complaints of back pain and increasing fatigue over the last 4 months. For the past week, his back pain seems to have worsened. It radiates to his legs and is burning in nature, 6/10 in intensity. There is no associated tingling sensation. He has lost 4.0 kg (8.8 lb) in the past 2 months. There is no history of trauma. He has hypertension which is well controlled with medications. Physical examination is normal. Laboratory studies show normocytic normochromic anemia. Serum calcium is 12.2 mg/dL and Serum total proteins is 8.8 gm/dL. A serum protein electrophoresis shows a monoclonal spike. X-ray of the spine shows osteolytic lesions over L2–L5 and right femur. A bone marrow biopsy reveals plasmacytosis. Which of the following is the most preferred treatment option?

Chemotherapy and autologous stem cell transplant

An investigator studying targeted therapy in patients with gastrointestinal stromal tumors requires a reliable test to determine the spatial distribution of CD117-positive cells in biopsy specimens. Which of the following is the most appropriate test?

Fluorescence in-situ hybridization

A 5-year-old boy is brought to the pediatric clinic for evaluation of fever, pain, swelling in the left leg, and limping. Review of systems and history is otherwise unremarkable. The vital signs include: pulse 110/min, temperature 38.1°C (100.6°F), and blood pressure 100/70 mm Hg. On examination, there is a tender swelling over the lower part of his left leg. Which 1 of the following X-ray findings is most suggestive of Ewing’s sarcoma?

X-ray showing lytic bone lesion with periosteal reaction

Mixed lytic and blastic appearance in the X-ray

X-ray showing broad-based projections from the surface of the bone

X-ray showing a sharply marginated radiolucent area within the apophysis

X-ray showing deep muscle plane displacement from the metaphysis

A 13-month-old boy with sickle cell anemia is brought to the emergency department because of continuous crying and severe left-hand swelling. His condition started 2 hours earlier without any preceding trauma. The child was given diclofenac syrup at home with no relief. The temperature is 37°C (98.6°F), blood pressure is 100/60 mm Hg, and pulse is 100/min. The physical examination reveals swelling and tenderness to palpation of the left hand. The hemoglobin level is 10.4 g/dL. Which of the following is the best initial step in management of this patient condition?

Magnetic resonance imaging (MRI) of the affected joint

A 1-month-old boy is brought to the physician because of a 5-day history of generalized fatigue and multiple episodes of vomiting which is most pronounced after formula feeding. His vomiting progressed from 2–3 episodes on the first day to 6–8 episodes at present. The vomitus is whitish in color. The mother reports that he has been very hungry after each episode of vomiting. The patient was born at 38 weeks' gestation and weighed 3100 g (6 lb 13 oz); he currently weighs 3500 g (7 lb 11 oz). He appears irritable. His temperature is 37.1°C (98.8°F), pulse is 130/min, respirations are 43/min, and blood pressure is 74/36 mm Hg. Examination shows dry mucous membranes. The abdomen is soft and not distended. There is a round mass palpable in the epigastric region. The liver is palpated 1 cm below the right costal margin. Laboratory studies show: Hemoglobin 15.3 g/dL Leukocyte count 6300/mm3 Platelet count 230,000/mm3 Serum Na+ 133 mEq/L K+ 3.4 mEq/L Cl- 92 mEq/L Glucose 77 mg/dL Creatinine 1.0 mg/dL A urinalysis shows a decreased pH. Which of the following is the most appropriate next step in the management of this patient?

Administer IV 0.9% NaCl and replace electrolytes

Perform emergency pyloromyotomy

Obtain CT scan of the abdomen with contrast

A 4-year-old boy with Down syndrome presents with fatigue and recurrent infections. CBC shows WBC 150,000/μL with 90% myeloblasts, hemoglobin 6.5 g/dL, platelets 15,000/μL. Flow cytometry confirms acute myeloid leukemia with megakaryoblastic features (AMKL). The parents are concerned about treatment intensity given their child's baseline developmental delays and increased treatment-related toxicity risk in Down syndrome. Evaluate the treatment approach considering the unique biology and competing risks.

Modified chemotherapy protocol with dose reductions of cytarabine but standard anthracyclines, given Down syndrome-associated AML excellent prognosis

Bone marrow transplantation as first-line therapy

Palliative care approach given poor baseline function and high treatment toxicity

Reduced-intensity chemotherapy due to Down syndrome and baseline developmental concerns

Standard AML chemotherapy protocol without modification

A 15-year-old boy presents with right distal femur pain and a palpable mass. X-ray shows a mixed lytic-sclerotic lesion with periosteal elevation creating a Codman triangle and sunburst pattern. Biopsy confirms osteosarcoma. Staging shows pulmonary micrometastases. Alkaline phosphatase is markedly elevated. The family requests consideration of alternative therapies and limb salvage options. Synthesize the treatment plan addressing oncologic outcomes and functional preservation.

Neoadjuvant chemotherapy, tumor necrosis assessment, limb salvage with endoprosthesis, and adjuvant chemotherapy with potential pulmonary metastasectomy

Limb salvage surgery without chemotherapy followed by observation

Radiation therapy alone as primary treatment

Palliative care focus given metastatic disease at presentation

Immediate amputation without chemotherapy due to metastatic disease

A 2-year-old girl presents with a large abdominal mass, aniridia, and developmental delay. Family history reveals a sibling who died of Wilms tumor at age 3. Genetic testing shows a germline WT1 mutation. Ultrasound reveals bilateral renal masses. The parents are concerned about treatment options that preserve renal function. Evaluate the optimal management strategy considering long-term outcomes.

Bilateral renal biopsy followed by neoadjuvant chemotherapy and bilateral nephron-sparing surgery

Chemotherapy followed by bilateral nephrectomy and immediate transplantation

Close surveillance with delayed intervention until symptoms develop

Immediate bilateral nephrectomy with dialysis and future transplantation

Unilateral nephrectomy of the larger tumor followed by observation of contralateral kidney

Osteosarcoma for USMLE Step 2 CK: High-Yield Pediatrics Lessons

Epidemiology & Pathogenesis - Big Bone Badness

Most common primary bone malignancy in children & adolescents.
Peak incidence: 10-20 years, linked to rapid bone growth (growth spurt).
Arises in the metaphysis of long bones from primitive mesenchymal cells.
Common sites: Distal femur > proximal tibia > proximal humerus.
Associated with genetic mutations: RB1 (Retinoblastoma) & TP53 (Li-Fraumeni syndrome).

⭐ The classic X-ray findings are a "sunburst" pattern and Codman's triangle.

X-ray: Osteosarcoma with Codman triangle & sunburst pattern

Clinical & Radiographic Features - Telling Pictures

Presentation: Localized pain & swelling, often worse at night. Palpable, tender, fixed bony mass. Pathological fractures can occur.
Location: Metaphysis of long bones, esp. around the knee (distal femur > proximal tibia > proximal humerus).
X-Ray Findings (Classic Triad):
- Sunburst appearance: Spiculated periosteal reaction.
- Codman's triangle: Triangular elevation of the periosteum.
- Destructive, ill-defined mixed lytic & sclerotic lesion.

⭐ Exam Favourite: Most common site is the metaphysis of a long bone, with ~60% of cases occurring around the knee.

X-ray: Osteosarcoma of distal femur with Codman triangle

Histopathology & Staging - Grading the Enemy

Biopsy is gold standard. Confirms diagnosis by showing malignant spindle-shaped stromal cells producing immature osteoid (lace-like pink matrix).
Subtypes: Conventional is most common (osteoblastic, chondroblastic, fibroblastic). Others include telangiectatic, small cell, and surface (parosteal/periosteal).
Staging (Enneking): Based on Grade (G), local Tumor extent (T), and Metastasis (M).
- G1: Low grade; G2: High grade
- T1: Intracompartmental; T2: Extracompartmental

Histopathology of osteosarcoma showing malignant osteoid

⭐ The most common site of metastasis is the lung, followed by bone.

Management & Prognosis - Attack & Rebuild

Standard of care is multi-modal: Neoadjuvant Chemo → Surgery → Adjuvant Chemo.
📌 Chemotherapy Regimen (MAP):
- High-Dose Methotrexate (with Leucovorin rescue)
- Adriamycin (Doxorubicin)
- Platinum (Cisplatin)
Surgery: Wide local excision. Limb salvage surgery (LSS) is now the standard over amputation where feasible (neurovascular bundle is free).

⭐ The single most important prognostic factor is the degree of tumor necrosis after neoadjuvant chemotherapy. A good response (>90% necrosis) correlates with a much better outcome.

High‑Yield Points - ⚡ Biggest Takeaways

Most common primary bone malignancy in adolescents, typically affecting the metaphysis of long bones, especially around the knee.

Classic X-ray findings include Codman's triangle and a "sunburst" pattern.

Histopathology reveals malignant osteoid formation by tumor cells.

Strongly associated with hereditary retinoblastoma (RB1 gene) and Li-Fraumeni syndrome (TP53).

The lungs are the most frequent site of distant metastasis.

Standard treatment is neoadjuvant chemotherapy followed by wide surgical resection.

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Osteosarcoma