Modified two-dimensional response as surrogate marker of overall survival in patients with metastatic colorectal cancer

The identification of surrogate markers for long-term outcomes in patients with metastatic colorectal cancer (mCRC) may help in designing treatment regimens. The aim of this study was to assess whether two-dimensional response (2-DR) can serve as a new surrogate marker for overall survival (OS) in patients with mCRC. The study group consisted of 99 patients with mCRC from two independent cohorts who were treated with oxaliplatin-based chemotherapy plus bevacizumab. Two-dimensional response was defined as an area enclosed by coordinate points, including early tumor shrinkage at 8weeks, depth of response at nadir, and 20% increase over nadir at progression. Each variable was weighted by its contribution rate to OS. The model was developed and internally validated in the learning cohort, and the performance of this model was externally verified in the validation cohort. Spearman correlation coefficients for 2-DR and OS in the learning and validation cohorts were 0.593 and 0.661, respectively. The C-indexes in predicting OS were 0.724 (95% confidence interval, 0.623-0.815) in the learning cohort and 0.762 (95% confidence interval, 0.651-0.873) in the validation cohort. Overall survival was significantly longer in patients with high 2-DR values than in patients with low 2-DR values in both the learning (37.0 vs. 24.1months, P<0.001) and validation (41.2 vs. 20.4months, P<0.001) cohorts. In contrast, differences in early tumor shrinkage and depth of response were not statistically significant. Multivariate analyses showed that 2-DR was an independent prognostic factor for OS.