Abstract Breast cancer (BC) is the most common malignancy diagnosed in adolescents and young adults (AYAs), with nearly 13,000 new cases diagnosed among women younger than 40 in the United States each year. Because AYAs are generally treated aggressively and are diagnosed at a time in their lives when having BC is non- normative, treatment can be extraordinarily disruptive and AYA survivors are more likely to suffer medically and psychosocially after a BC diagnosis than older women. While many acute symptoms resolve following initial treatment, the long-term physical, emotional and psychosocial impact on a young woman’s life trajectory may worsen or only become evident in survivorship. Our team and others have documented the unmet needs of AYA BC survivors in symptom management (e.g., sexual problems, anxiety, fatigue, stress, depression, sleep problems, hot flashes, musculoskeletal complaints), as well as AYA concerns, defined as concerns unique to or accentuated by being young at diagnosis (e.g., fertility/family planning, genetics, finding life partners, childrearing, body image and sexuality, and educational and economic attainment). Beyond causing distress, AYA BC concerns and symptoms influence longer-term treatment decisions, including adherence to risk- reducing adjuvant endocrine therapy and health behaviors. Thus, improved attention to AYA BC concerns and symptoms in survivorship may improve not only symptom management and quality of life (QOL), but disease and overall mortality outcomes. However, the health care system is not equipped to meet the needs of AYA patients who are struggling with subacute symptoms and concerns following the completion of active treatment. Strategies to empower patients with the tools and support they need to fully recover and to improve well-being are needed. Serial symptom monitoring using electronic patient-reported outcomes systems has resulted in greater attention to and better management of symptoms, and improved QOL and survival in adults receiving chemotherapy. We have adapted this model and designed, piloted, and refined the Young, Empowered and Strong (YES) portal, a mobile health (mHealth) intervention for AYA BC survivors. YES is a multicomponent intervention to engage and activate AYA BC survivors to self-monitor and self-manage AYA concerns and symptoms, outside of the clinical setting, by providing tailored information, resources and support. For additional psychosocial support, YES provides an expressive writing platform as well as a monitored “chat room” for young survivors to connect with each other. In the proposed research, we will test the YES portal compared to usual care in a 3 site randomized clinical trial of 360 geographically and racial-ethnically diverse young BC survivors from the Dana-Farber Cancer Institute, The Ohio State University, and Columbia Univeristy Medical Center. We expect this novel mHealth intervention will reduce overall symptom burden and unmet AYA concerns and improve quality of life, and will be utilized and valued by a diverse population of AYA BC survivors.

Project Narrative Adolescent and young adult (AYA) breast cancer survivors experience substantial symptoms and have unmet concerns in survivorship. In the proposed multi-site RCT, we will test the efficacy of YES, a novel mHealth self- management intervention designed to address the needs of AYA breast cancer survivors vs. usual care. We hope YES will reduce diverse survivors’ symptoms and concerns and improve their quality of life.