PURPOSE:  Estimating the value of an oncology treatment is challenging due to frequent immature trial data, the need for statistical extrapolation of survival, and assumptions on quality of life, treatment patterns and resource use. Typically, a survival-partition approach is employed, dividing patients into three health states based on overall survival and progression-free survival. The emergence of immuno-oncology (IO) agents and their new mechanism of action add further layers of complexity in the assessment of value. The objective of this workshop is to discuss additional challenges in modeling IO treatments, building upon a workshop assessing survival projection methods for IO agents, presented at ISPOR EU. Specific aims include assessing modeling challenges from a clinical and health economic perspective, evaluating current solutions and proposing new ones. DESCRIPTION:  Attendees will be introduced to relevant differences in IO treatments compared to chemotherapies by a clinician experienced with IO therapies in trials and clinical practice. Key differences between IO therapies and chemotherapies, including the relevance of standard definitions of disease progression for predicting patients’ quality of life, treatment duration, resource use, and long-term outcomes will be discussed. Next, the challenges resulting from these differences and a review of recent models assessing IO agents will be presented. Both standard and alternative methodological approaches used to date to address IO-specific data gaps and uncertainties alongside strengths and weaknesses will be examined and recommendations will be provided for potential new model structures. Finally, the resulting challenges for assessing the economic value of IO therapies, including estimating long-term outcomes, evaluating comparative efficacy (CE), estimating long-term treatment costs and quality of life will be discussed. Attendees will be invited to contribute their experiences with developing or reviewing CE models of IO treatments, and asked to respond to questions about the new challenges of assessing the value of these therapies.