USMLE Step 1 Question 365

Question:

A 16-year-old African-American boy presents to his primary care physician complaining of leg swelling for the past several months. Exam reveals a large, tender soft tissue mass just proximal to the knee. Of note, he is found to have lost 8 lbs and has a hemoglobin level of 11.0 g/dL. Plain film demonstrates periosteal elevation with bone destruction; a biopsy is performed. Which of the following describes the expected pathology specimen?

Correct Answer: C.  Large, necrotic, hemorrhagic mass with osteoid and bone

With regards to race, age, gender, complaint, duration, and location, this patient demonstrates a classic presentation the most common primary bone tumor: osteosarcoma. (Systemic symptoms are variable.) Presence of osteoid is the defining characteristic for all types of osteosarcoma. Large, necrotic, hemorrhagic mass with osteoid and bone (choice C) is correct.

Brown nodule surrounded by dense sclerotic cortical bone (choice A) is seen with osteoid osteoma. This condition would not demonstrate the radiological findings described.

Dense normal bone with cartilaginous cap (choice B) describes an exostosis of a benign osteochondroma. This growth would be visible on x-ray, and does not lead to periosteal elevation or bone destruction.

Myxomatous tissue (choice D) is seen in lesions of chondromyxoid fibroma; however, these lesions are usually intramedullary rather than cortical.

Neoplastic colon tissue (choice E) could be seen with metastatic colon cancer, but is unlikely in this patient due to his age. Further, among metastatic cancers, colon is least likely to metastasize to bone.