11120 Background: Anxiety is one of the most commonly reported symptoms among cancer patients, and is a known risk factor for reduced health-related quality of life and other negative patient-reported outcomes (PROs). Mobile health applications (apps) are tools that can be used flexibly in patients’ preferred environments with the potential to reduce anxiety and improve quality of life. The current study sought to examine the feasibility and preliminary efficacy of a mobile audio companion app, Elly, to improve anxiety and other critical PROs among cancer patients. Methods: This was a single-site, single-arm pilot study conducted over 6-months. Adults 18 years or older with a diagnosis of cancer of any type, received treatment within 6 months of consent, and had access to an iPhone were eligible. The primary outcome was change in mean anxiety t-scores (NIH PROMIS anxiety short form (8a)) administered electronically via REDCap at baseline, 1 (primary timepoint), 3, and 6 months. Secondary outcomes included changes in NIH PROMIS depression, loneliness, social support, and perceived stress scores from baseline to 6 months. Changes in NIH PROMIS T-scores at each time point were calculated and analyzed using paired t-tests. Results: Of 53 patients who consented for the study, 38 patients (72%) were included in the analysis ( Mage: 52.8 years, SD: 11.7, 84.2% female). Most participants reported a history of breast cancer (50%), followed by ovarian (16%), hematologic (11%), and other cancer types (24%) Phone incompatibility and technological challenges were the most common reasons for screen-fails (n=15). All participants downloaded and used the app at least once, with an average of 154 app usage events across participants recorded over the study period (median: 64, range 11-1186 times). The mean baseline anxiety T-score was 63.5 (SD: 2.1). Anxiety levels decreased among participants over time, with a mean difference in anxiety T-scores of -1.9 at 30 days, -3.3 at 90 days, and -3.0 at 6 months from baseline, which was statistically (p<0.05) and clinically significant. Participants also reported improvements in perceived stress, depression symptomatology, social support, and loneliness, although statistical significance was not reached. Conclusions: Mobile apps, such as Elly, may feasibly be used to support patient-reported anxiety as well as other PROs, especially among those who present with high levels of anxiety at baseline. Efforts to increase access to mobile health apps and provide technical support for patients should be made increase equity across the cancer survivor population. Larger, multi-center randomized controlled trials are needed to build on these findings.