Subjects who are randomized to the CDC mobile app treatment arm will be asked to perform the app's full suite of intervention tools such as learning about PTSD, assessment, finding support, and mind/body exercises (e.g., guided imagery, meditation, and relaxation exercises) over the entire 8-week study period.

Subjects who are randomized to the CDC mobile app wait-list control arm will be asked to perform only the learning about PTSD, assessment, and finding support activities for the first 4 weeks. Following completion of the Week-4 questionnaires, subjects will then be asked to additionally perform the mind/body exercises (e.g., guided imagery, meditation, and relaxation exercises) for the duration of the 8-week study period.

Cancer Distress Coach is a stand-alone symptom management tool with three basic components. The Learn about Distress module provides psycho-education. The Insights module includes an inspiring Quote of the Day, daily activity planning tips, a graph displaying the user's distress level plotted over time, and assessment feedback. The main action of the application is in the Activities module that provides patients with skills to manage their stress in the moment they experience it. Depending on the severity, the patient is routed to any of a number of helpful skills based on cognitive-behavioral principles. The stress management tools include positive imageries, soothing songs and pictures, and the Relax-Identify-Decide tool. Also included is "find support" and "get support now" to connect the user to his/her support network and locate informal cancer and non-cancer related support or (immediate) professional care.

The PCL-5 is a 20-item self-report symptom checklist that closely mirrors DSM-5 diagnoses criteria. The instructions will be modified so that symptoms are keyed to the particular traumatic stressor of interest; specifically, subjects will be asked to rate each PTSD symptom in the past 4 weeks with respect to their cancer diagnosis and treatment.

The Distress Thermometer is used to assess psychosocial distress. It consists of a one-item self-report scale from 0-10, where 0 represents no distress and 10 represents extreme distress.

The Feedback questionnaire was developed by the study team to assess perceived helpfulness of the app and user satisfaction with the app. Points are totaled and summed.