A 15-year-old boy is brought to the emergency department due to hemoptysis. He has a history of amputation of the right lower extremity for "bone cancer" in Mexico. Chest imaging reveals a lung mass. Excisional biopsy of the mass shows sheets of uniform, small (slightly larger than lymphocytes), round cells with scant, clear cytoplasm. The cellular deposits are interrupted by vascular fibrous septae, with areas of hemorrhage and an abrupt transition from viable to necrotic cells. A representative sample is shown in the image. Which of the following is the most likely diagnosis?

Question

A 15-year-old boy is brought to the emergency department due to hemoptysis.  He has a history of amputation of the right lower extremity for "bone cancer" in Mexico.  Chest imaging reveals a lung mass.  Excisional biopsy of the mass shows sheets of uniform, small (slightly larger than lymphocytes), round cells with scant, clear cytoplasm.  The cellular deposits are interrupted by vascular fibrous septae, with areas of hemorrhage and an abrupt transition from viable to necrotic cells.  A representative sample is shown in the image.  Which of the following is the most likely diagnosis?

Quizplus · Accepted Answer

11ec160b_3a55_41d5_9249_ed715e37728b_MD0001_00 This boy with a history of bone cancer has a lung tumor with sheets of uniform, small, round cells, raising strong suspicion for metastatic Ewing sarcoma (ES). ES is the second most common childhood bone malignancy (after osteosarcoma) and typically presents with pain and swelling at the bone tumor site. Spread to the lungs or other tissue can occur in those who don't undergo both resection and chemotherapy. ES is a primitive, undifferentiated tumor that was originally thought to be neuroectodermal in origin but is now believed to arise from a mesenchymal stem cell. Tumor histology typically reveals sheets of uniform, small, round, cells with clear, scant cytoplasm separated by fibrous septae and patches of necrosis/hemorrhage. This appearance resembles neuroendocrine tumors such as carcinoid and small cell lung cancer. Most cases of ES involve translocations of EWSR1 and FLI1. (Choice A) Adenocarcinoma, the most common primary lung malignancy, often metastasizes to bone. However, histopathology would show neoplastic glands lined by mucin-producing cells. (Choice B) Chondrosarcoma is an uncommon tumor and typically occurs in the 5th or 6th decade of life. Histology shows neoplastic chondrocytes in a hyaline cartilage matrix, usually with small calcifications. (Choice D) Multiple myeloma is a plasma cell malignancy that is extremely rare in patients age <40. X-ray often shows multiple lytic lesions, osteopenia, and pathologic fractures. The malignant cells have eccentric nuclei with "clock-face" chromatin, perinuclear clearing, and abundant basophilic cytoplasm. (Choice E) Osteosarcoma is the most common primary bone malignancy. Histology shows pleomorphic, spindle-shaped cells that produce new osteoid and bone. Educational objective: Ewing sarcoma is the second most common malignant bone tumor of childhood (after osteosarcoma). It most commonly involves the lower extremity and pelvis and often metastasizes to the lungs. Histopathology is characterized by uniform, small, round, cells; fibrous septae; and patches of necrosis and hemorrhage. __________ References: Pediatric malignant bone tumors: a review and update on current challenges, and emerging drug targets. (http://www.ncbi.nlm.nih.gov/pubmed/27265835)

A 15-Year-Old Boy Is Brought to the Emergency Department Due