Evaluation of relative dose intensity during the early phase of first-line sunitinib treatment using a 2-week-on/1-week-off regimen for metastatic renal cell carcinoma.

Sunitinib treatment with a 2-week-on/1-week-off schedule (Schedule 2/1) is a common alternative regimen with high relative dose intensity (RDI) and superior tolerability for patients with metastatic renal cell carcinoma (mRCC). The prognostic impact of RDI is reported only in 4-week-on/2-week-off or mixed regimens. Herein, we evaluated the prognostic impact of RDI during early-phase sunitinib treatment using Schedule 2/1. Seventy-four patients who received first-line sunitinib treatment using Schedule 2/1 were evaluated. Endpoints were progression-free survival (PFS) and overall survival (OS). We assessed RDI within the initial two cycles (2c-RDI), and its prognostic impact. Predictive factors for 2c-RDI deterioration were also evaluated. The cut-off value of 2c-RDI was set at 65%. Based on this cut-off, 31 patients (42.0%) were classified into the low 2c-RDI group (< 65%). PFS and OS were significantly shorter in the low-2c-RDI patients, compared with the high 2c-RDI patients (median PFS: 6.15 vs. 18.4 months, p = 0.0005; OS 11.0 vs. 39.3 months, p = 0.0002). Furthermore, multivariate analyses showed that the development of dose-limiting toxicities (DLTs) within the initial two cycles, as well as low initial dose, were independent factors for low 2c-RDI (DLTs: OR 18.6, 95% CI 3.27-105.30, p = 0.0010; initial dose: OR 9.26, 95% CI 1.42-60.40, p = 0.020). The most common adverse event was thrombocytopenia (any grade: 24.3%; grade ≥ 3: 8.1%). More than 65% of 2c-RDI should be maintained for optimal therapeutic effect of sunitinib treatment using Schedule 2/1. To achieve the appropriate 2c-RDI, careful follow-up for patient tolerability is needed to avoid early DLT development.