The goal of this is to validate the Patient-Reported Outcomes Measurement Information System (PROMIS) in sarcoma patients undergoing surgery, and to evaluate a novel smartphone app for collecting mobility data. The goals of the study include to: 1. Validate PROMIS as a patient outcome measure in sarcoma 2. Assess the effectiveness of a novel app for administering questionnaires and collecting mobility metrics 3. Compare PROMIS scores and mobility metrics to better evaluate recovery trajectories after surgery Participants will complete PROMIS questionnaires at regularly scheduled intervals using the smartphone app. Questionnaires will be completed pre-operatively and at 6 weeks, 12 weeks, 6 months, and 12 months post-operatively. Additionally, the app will passively track mobility metrics such as daily step count, stairs climbed, and gait parameters to compare with PROMIS scores.