You are answering a USMLE-style medical question. Question: A 65-year-old man presents with pain in his left thigh for a week. He describes the pain as dull and constant, boring in nature, and localized deep below the thigh muscle. He says it is worse at night. Physical examination is significant for tenderness and warmth over the anterior aspect of the left thigh. A plain radiograph of the left femur shows increased cortical thickness with widened intercortical space. Laboratory studies show: Alkaline phosphatase 925 U/L Serum calcium 9.2 mg/dL Serum phosphorus 4.4 mg/dL Findings on bone biopsy are shown in the image. Which of the following is the most likely diagnosis in this patient? Options: A) Ewing's sarcoma B) Osteitis deformans C) Osteochondritis dissecans D) Osteitis fibrosa cystica Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.