## Most Common Bone Site for Ewing Sarcoma **Key Point:** The **femur** is the single most common bone affected by Ewing sarcoma, accounting for approximately **25–30%** of all cases. The pelvis is the second most common site (20–25%), followed by the tibia (15–20%). ### Distribution of Ewing Sarcoma by Bone | Bone | Frequency | Notes | | --- | --- | --- | | **Femur** | 25–30% | Most common; long bone predilection | | **Pelvis** | 20–25% | Second most common; flat bone | | **Tibia** | 15–20% | Third most common | | **Fibula** | 5–10% | Less common | | **Humerus** | 5–10% | Upper limb involvement rare | | **Other sites** | <10% | Ribs, spine, small bones | **High-Yield:** Ewing sarcoma has a strong predilection for **long bones of the lower extremity** (femur + tibia + fibula account for ~50% of all cases). The **femur alone** is twice as common as the tibia and significantly more common than the humerus. ### Clinical Pearl When a young patient (10–25 years old) presents with a painful bone lesion, the femur should be the first bone to consider for Ewing sarcoma. However, the **pelvis is an important second site** — pelvic Ewing sarcomas often present late because they are deep and may be mistaken for other conditions (e.g., hip pain, referred pain from viscera). ### Why the Femur? 1. **Largest long bone** — greater bone mass and higher cell turnover 2. **Rapid growth** — particularly in adolescents during skeletal maturation 3. **Diaphyseal location** — Ewing sarcoma's characteristic site within the femur 4. **Proximity to knee** — major growth plate activity **Mnemonic: FTP (Femur, Tibia, Pelvis)** — the three most common sites for Ewing sarcoma, in order of frequency. [cite:Robbins 10e Ch 26]
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