Pazopanib Exposure Relationship with Clinical Efficacy and Safety in the Adjuvant Treatment of Advanced Renal Cell Carcinoma.

Purpose: PROTECT, a phase III, randomized, placebo-controlled study, evaluated pazopanib efficacy and safety in the adjuvant renal cell carcinoma setting. The relationship between pazopanib exposure (Ctrough) and efficacy and safety was evaluated.Patients and Methods: Evaluable steady-state blood trough concentrations were collected from 311 patients at week 3 or 5 (early Ctrough) and 250 patients at week 16 or 20 (late Ctrough). Pazopanib pharmacokinetic (PK) data were analyzed via a population model approach. Relationship between Ctrough or dose intensity and disease-free survival (DFS) was explored via Kaplan-Meier and multivariate analysis. Adverse events (AE) and AE-related treatment discontinuation proportions were summarized by Ctrough quartiles.Results: Most (>90%) patients with early or late Ctrough data started on 600 mg. Mean early and late Ctrough overlapped across dose levels. Patients with higher early Ctrough quartiles achieved longer DFS (adjusted HR, 0.58; 95% confidence interval, 0.42-0.82; P = 0.002). Patients achieving early or late Ctrough >20.5 µg/mL had significantly longer DFS: not estimable (NE) versus 29.5 months, P = 0.006, and NE versus 29.9 months, P = 0.008, respectively. Dose intensity up to week 8 did not correlate with DFS, consistent with population PK model-based simulations showing overlapping pazopanib exposure with 600 and 800 mg doses. The proportion of AE-related treatment discontinuation and grade 3/4 AEs, with the exception of hypertension, was not correlated to CtroughConclusions: In the adjuvant setting, higher pazopanib Ctrough was associated with improved DFS and did not increase treatment discontinuations or grade 3/4 AEs, with the exception of hypertension. Clin Cancer Res; 24(13); 3005-13. ©2018 AACRSee related commentary by Rini, p. 2979.