PROJECT SUMMARY Providing care to a loved one with a severe illness is not a normative task for young adults. Yet, approximately 1.46 million young adults provide informal care for a cancer patient. Among young adult cancer caregivers, an unexpected caregiving role can lead to fear of abandonment and loss. Furthermore, caregiving is uniquely burdensome to young adults because they take on this new role amidst multiple existing responsibilities and developmental transitions of young adulthood (e.g., completing education, establishing a career, developing intimate relationships, attaining financial stability). On the other hand, young adult cancer caregivers who feel supported by their social networks may be protected from becoming overburdened, especially during the acute period of transition to becoming a caregiver. Widespread use of social media among young adults demands recognition of a changing social world in the 21st century and underscores the necessity of studying social support in existing online networks. In 2014, 89% of young adults in the United States used social media (e.g., Facebook, Twitter) to seek answers to questions about health, share information, and foster relationships. Social support mediates depression, loneliness, and burden among cancer caregivers. Social media use may enhance young adult cancer caregivers' ability to garner different types of functional social support (emotional, instrumental, information, companionship, validation). However, if social support originates from inappropriate sources or in undesired forms it may be detrimental to young adults' ability to cope with new caregiving responsibilities. Therefore, our long-term goal is to improve the acquisition of social support through social media among young adult cancer caregivers. To this end, we have devised an innovative approach to studying the acquisition of social support through social media among young adult cancer caregivers during the first six months of caregiving, an acute period of transition to a caregiving role. This proposal addresses three critical objectives in young adult cancer caregiving research by: evaluating the feasibility of studying social support through social media in this population, defining the acquisition of social support through social media including the change in social support over time as a caregiver, and informing a future social media intervention for caregivers. A mixed methods study is proposed including semi- structured interviews, technology-based text-mining content analysis, and longitudinal predictive modeling to study mediators and moderators of social support acquisition. The findings will inform an intervention to coach young adult cancer caregivers on leveraging social media to acquire sustained functional social support. This research has implications for supporting young adult caregivers of patients with other diseases in social media research and clinical supportive services.