Correlating Surrogate Endpoints with Overall Survival at the Individual Patient Level in BRAFV600E-Mutated Metastatic Melanoma Patients Treated with Vemurafenib.

Purpose: Surrogate endpoints are needed that correlate with overall survival (OS). We analyzed individual patient tumor data from a phase III trial of vemurafenib versus 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).

Experimental Design: Deidentified tumor measurements and OS data from BRIM3 and from BRIM2 were analyzed. Target tumor measurement data and nontarget tumor data were available from pretreatment, weeks 6,12, and every 9 weeks thereafter. In the BRIM3 data set, associations of OS with both early tumor response (first 12 weeks) and time to progression (TTP) were assessed. Different definitions of response and progression were explored. Findings were validated using the BRIM2 data set.

Results: Thresholds of early response were explored ranging from any degree of tumor shrinkage to 100% tumor shrinkage. Correlation was weak at all thresholds tested. TTP, however, was more strongly correlated with OS. The strongest correlation was seen when progression was defined as ≥50% increase in the sum of tumor diameters or appearance of new tumors. This was confirmed by similar analyses in the BRIM2 cohort.

Conclusions: TTP defined as ≥50% increase in the sum of tumor diameters or appearance of new tumors was more strongly associated with OS than early tumor shrinkage in melanoma patients treated with RAF inhibitor. In future trials, consideration should be given to replacing response rate with TTP or PFS as preferable clinical endpoints in early-phase studies.