Chest Wall Ewing Sarcoma Presenting as Abdominal Pain in a 12-Year-Old Boy

A 12-year-old boy presented with a 3-month history of right upper quadrant abdominal pain, a 15%-20% loss of body weight, and a 3-week history of cough and dyspnea. He did not have jaundice, fever, acholic or melanotic stools, or nausea/vomiting. Respirations were 40/minute and regular, and heart ratewas 125 beats/minute. Heart sounds and point of maximum impulse were displaced to the left. He exhibited increased work of breathing, with absent breath sounds on the right side and diffuse crackles on the left side. Examination revealed a palpable 10 8 cm, firm, immobile, nontender subcutaneousmass protruding from the right side of the back. Laboratory studies were significant only formild normocytic anemia (hemoglobin, 9.4 g/dL, mean corpuscular volume, 75 fL) and mildly elevated serum lactic dehydrogenase (422 U/L) and uric acid (7.3 mg/dL) levels. Imaging revealed a large mass in the right hemithorax with associated pleural effusion, mediastinal shift, and protrusion posteriorly through the ribcage (Figure, A, B, and C). Biopsy analysis showed a small, round blue cell tumor strongly positive for CD99