A 15 year old boy is presenting for unilateral left leg pain with limp for the past 5 weeks. He has no past medical history. He had trauma when playing soccer  a week prior to the symptoms. The pain is dull and mainly over night. The patient has no fever. Review of systems (ROS) reveals fatigue but no night sweats or weight loss. The joint exam shows a palpable mass over the left tibia. Labs show an elevation of LDH and alkaline phosphatase. Patient had normal ESR, CRP and CBC.