A.K., a 14-year-old male, began experiencing pain in his lower left leg during a period of intense training for a world-class cycling event. Thinking it was due to overexertion, he did not initially seek treatment, instead treating it with RICE—rest, ice, compression, elevation—and pushing through the pain to compete. When he limited his training following the race and the pain remained, he visited his pediatrician. A.K. was otherwise systemically well. He did not have any fevers or weight loss. Other than his leg pain, he had no other complaints. The pediatrician sent him to a sports medicine specialist.

On examination, he had full range of motion of the left knee and mild tenderness over the upper tibia. There was no discrete mass. He had normal strength and sensation in the extremity. An X-ray was concerning for a lesion in the upper tibia. An MRI was ordered, and it confirmed a 17-cm marrow infiltrative process in the proximal portion of the tibia. There was a small soft tissue component extending from the tibia. Based on the MRI results, A.K. was referred to Children’s Hospital of Philadelphia for further evaluation.

What is the most likely diagnosis?

Have you figured out this issue’s diagnosis? The correct answer is osteosarcoma, the subject of the Winter 2018 cover article.

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