3-month Gradually Enlarging in Surgery — 52yo Man | Orthopedics | SMLE Q#9473

A 52-year-old man presents to an orthopedic oncology clinic with a 3-month history of a gradually enlarging, firm, mildly tender mass in the anterolateral aspect of his right thigh. He denies trauma, fever, or weight loss. MRI of the thigh shows a 9-cm intramuscular mass within the quadriceps, suspicious for high-grade soft tissue sarcoma, abutting but not encasing the femur, with no clear fat plane for simple excision. There is no evidence of distant metastasis on staging CT. Which of the following is the most appropriate biopsy technique to establish the diagnosis before planning definitive limb-sparing surgery?