PTPRF expression was found to be prognostic for shorter overall survival but was also significantly predictive of improved survival with erlotinib versus placebo in SATURN (hazard ratio, 0.45 [95% confidence interval, CI, 0.30–0.69] in PTPRF high versus 0.96 [95% CI, 0.62–1.48] in PTPRF low; interaction p = 0.02)...PTPRF may have value as a predictive marker to identify which patients can obtain the greatest benefit from erlotinib in the post–first-line setting.