Objective smartphone measurements of physical activity and fitness in patients with cancer

132 Background: Optimal (study) treatment for patients with advanced cancer is influenced by their performance status (PS) before initiation of systemic therapy. An objective assessment of a patient’s physical function is difficult to make and is currently heavily depending on the estimation of their PS by the treating physician. Objectively measured physical activity (PA) and physical fitness (FIT) may be more predictive for survival and treatment tolerability than their PS. We hypothesize that an objective measurement may provide more accurate estimates of a patient’s physical function and thereby a better outcome of (study) treatment. Unfortunately, routine objective measurements are time consuming and costly. Therefore, we aimed to investigate the validity and reliability of smartphone measurements of PA and FIT in patients with cancer. Methods: At present, 56 ambulant patients with various types of cancer participated. Patients wore an accelerometer for 7, and an IPhone for 14 consecutive days to measure the mean number of steps per day. Patients performed a 6MWT twice with the use of an smartphone application in their home environment and once in a test environment in the hospital. To assess the validity, we calculated the intraclass correlation coefficient (ICC) between the accelerometer and the first week of the IPhone for PA, and between the 6MWT in the hospital and the home environment for FIT. To assess reliability, we calculated the ICC between the IPhone week 1 and 2 for PA, and between the first and second 6MWT in the home environment for FIT. Results: Validity was excellent for PA (ICC = 0.96,p < 0.05) and low for FIT (ICC = 0.33,p < 0.05). We found excellent reliability for PA (ICC 0.94,p < 0.05) and FIT (ICC = 0.93,p < 0.05). Conclusions: In this study we found that objective smartphone measurements of PA are valid and reliable. FIT assessments were reliable, but in its present form its validity was low. A prospective study has been initiated to investigate whether objectively measured PA and/or FIT, better predicts early trial discontinuation and survival than PS or patient-reported physical function.