We report on the usability of a mobile application, MyPath, that connects patients with personalized information based on their diagnosis and care plan and adapts over time as they progress through the cancer trajectory. We conducted usability tests with cancer survivors and health professionals, measuring three usability factors which could be affected by adaptive content: learnability, errors, and effectiveness. Our results indicate that the adaptive information did not obstruct usability of the system. Participants identified several strengths of the application, including the integration of clinical and non-clinical information, the segmentation of a large information set to reduce mental burden, and the inclusion of multiple media types to accommodate different learning styles. Participants also identified potential barriers to use and offered ideas for future developments. We share how we integrated this feedback into the MyPath system design and reflect on lessons for future personal health information systems.