Review Question - QID 219346

A 50-year-old male was referred to a musculoskeletal oncologist after being hit in the shin with a softball during a corporate retreat. He had unrelenting pain for several weeks after the incident, and radiographs demonstrated a subtle lesion in his tibial shaft, prompting his internist to order the MRI shown in Figure A. The patient notes that he has incidentally felt increasingly fatigued over the last six months, has lost nearly 18 pounds over the same period, and notes that his wife has had to turn the thermostat down to 65 degrees to keep him from sweating through the sheets at night. A biopsy of the patient's tibial lesion is recommended and is shown in Figure B. For which of the following immunohistochemical stains would this tumor most likely stain positive?