A cancer diagnosis and its subsequent treatment affects whole patient health -- disrupting the full spectrum of physical, social, emotional, and functional quality of life. An estimated 83% of cancer patients report low to very low quality of life. Individuals receiving chemotherapy report experiencing over 13 concurrent symptoms, including fatigue, sleep difficulties, and pain. 30%-40% of people with cancer report significant psychological symptoms, including anxiety and depression. Such disruptions in mental health and quality of life, in turn, exacerbate physical symptoms and can worsen clinical outcomes. Despite growing evidence of the complex, interconnected pathways linking the mind and body, scalable interventions that efficiently target whole-person health upon diagnosis of a life-altering disease such as cancer have not yet been developed. Existing medical treatments, focus on the physiological aspects of the disease. Existing psychological treatments, such as Cognitive Behavior Therapy (CBT) and Mindfulness Based Stress Reduction (MBSR), apply a broad range of cognitive and behavioral strategies to reduce diffuse symptoms of depression and anxiety. Such ancillary programs for psychological care are routinely proposed as methods to reduce distress and symptoms, restore function, and improve quality of life, but they are frequently inaccessible to patients and notoriously difficult to scale. The MINDSET intervention aims to close this major treatment gap and promote whole patient health by targeting patient mindsets at the point of diagnosis. This proposal builds on our extensive foundational research completed over the past 6 years with support of the NIH New Innovator Award (DP2 AT009511) to test a novel mHealth intervention targeting patient mindsets at the point of diagnosis. In our prior research, we showed that a 2.5-hour digital MINDSET intervention significantly improves whole patient health (physical, social, and emotional functioning as measured by the FACT-G) in patients undergoing systemic treatment for cancer with curative intent compared to a Treatment as Usual (TAU) control. Leveraging our interdisciplinary team of experts in oncology, psychology, psychiatry, mHealth, and biostatistics, we aim to expand on this prior research to address this large and costly gap in clinical care. We propose a fully decentralized Phase 3 randomized controlled trial in which 440 cancer patients treated for non-metastatic solid tumors and hematological malignancies will be allocated to either a (1) MINDSET or (2) Matched Attention Control (MAC) condition. Patient-reported primary outcomes (FACT-G Total Score) and secondary outcomes (anxiety, depression, affect, sleep, coping, symptom distress, patient activation/engagement, and inflammatory biology) will be assessed at weeks 0 (baseline), 2, 4, 6, and 10. Durability of the effect of the intervention will be measured at two follow-up timepoints: 3 months, and 6 months after study completion. By promoting health at the psychological, behavioral, and biological levels, MINDSET interventions have the potential to become a highly impactful and complementary tool for promoting whole patient health.