e20020 Background: Surrogate endpoints are needed that correlate with overall survival (OS). We analyzed individual patient tumor data from a phase III trial of vemurafenib vs. dacarbazine (BRIM3) to identify criteria for tumor measures that correlated with OS. Correlates were validated using a separate data set from a phase II trial of vemurafenib (BRIM2). Methods: De-identified tumor measurements and OS data from BRIM3 and BRIM2 were analyzed. Target and non-target tumor measurement data were available from pretreatment, weeks 6 and 12, and every 9 weeks thereafter. In BRIM3, associations of OS with both early tumor response (first 16 weeks) and time to progression (TTP) were assessed using a normalized concordance probability estimate and Kendall’s tau derived from the Clayton copula, respectively. Different definitions of response and progression were explored. Findings were validated using BRIM2. Results: Thresholds of early response were explored ranging from any degree to 100% tumor shrinkage. Corr...