Effect of the timing of best tumor shrinkage on survival of patients with metastatic renal cell carcinoma who received first-line tyrosine kinase inhibitor therapy.

Background: To evaluate the association between the timing of best tumor shrinkage (bTS) and metastatic renal cell carcinoma (mRCC) patient survival after first-line tyrosine kinase inhibitor (TKI) therapy.
Methods: The tumors of 91 patients with mRCC showed a response to TKIs. None of the patients had received prior cytokine therapy. The magnitude of bTS was categorized according to the Response Evaluation Criteria in Solid Tumors v. 1.1. The patients were divided into two subgroups according to the timing of bTS: early responders (≤3 months) and late responders (>3 months). Overall survival (OS) and progression-free survival (PFS) after first-line TKI therapy were evaluated, and factors predicting survival were examined.
Results: Sunitinib, sorafenib, and pazopanib were used in 62, 25, and 4 responders, respectively. In total, 52 (57.1 %) and 39 (42.9 %) patients were early and late responders, respectively. Early responders had significantly lower PFS compared to late responders (median survival, 11.4 vs. 19.1 months; log-rank test, p = 0.0263), although there were no significant differences in the OS of early and late responders (27.0 vs. 30.1 months, p = 0.306). Multivariate analyses revealed that the timing of bTS was an independent predictor of PFS and OS (PFS, hazard ratio 4.09, p < 0.0001; OS, hazard ratio 2.32, p = 0.0107).
Conclusion: The timing of bTS was an independent predictor of survival in patients with mRCC who received first-line TKIs.