At the end of cancer treatment, many patients are still dealing with symptoms of cancer and side effects of treatment. Many are also left in a surreal mental state with uncertainty regarding the future of their health. Survivorship Care Plans are plans that are provided to individuals at the completion of cancer treatment (i.e., chemotherapy, surgery, radiation). Survivorship Care Plans describe the details of a person's diagnosis and treatment, as well as provide recommendations for follow-up appointments, referrals, and healthy behaviors to accelerate recovery and prevent recurrence (e.g., diet, exercise, smoking cessation). Survivorship Care Plans are currently static documents that are provided via paper and become outdated as soon as the person's health status changes. Therefore, there is a need to digitize Survivorship Care Plans to improve the accessibility, modifiability, and longevity of the plan. In addition, with current technology, there is an opportunity for Survivorship Care Plans to be linked with mobile devices and activity trackers so that people can track health behaviors and compare them to their clinical goals, enabling people to take charge of their own health. Charles River Analytics developed an app called POSTHOC (POST-treatment Healthcare Outcomes for Cancer survivors) that digitizes the Survivorship Care Plan with goals to integrate it into the digital medical record. Herein, phase I/II feasibility/preliminary efficacy randomized controlled trial is being conducted among 54 patients with cancer who recently completed adjuvant treatment for cancer (e.g., chemotherapy, radiotherapy, surgery) to compare 12 weeks of the POSTHOC app as part of the Survivorship Care Plan vs. the usual care Survivorship Care Plan on total symptom burden. Participants will be randomized 2:1, POSTHOC:usual care. Those randomized to the POSTHOC group will be provided with their Survivorship Care Plan via the app, and will choose to focus on nutrition or exercise for the duration of the study, based on their individual plan and personal preferences. At baseline, 6 weeks, and 12 weeks, patient-reported outcomes will be evaluated including total symptom burden, diet, and physical activity. Extensive quantitative and qualitative feedback will also be collected on the usability of the app from those in the POSTHOC arm in order to improve the app for future implementation studies.