Treatment-free survival outcomes from the phase II study of nivolumab and salvage nivolumab/ipilimumab in advanced clear cell renal cell carcinoma (HCRN GU16-260-Cohort A).

Background: As part of a partitioned survival analysis, treatment-free survival (TFS) can characterize the overall survival time patients spend between the cessation of immunotherapy and the start of subsequent therapy; both with and without toxicity. Significant TFS was reported for the nivolumab/ipilimumab arms of the CheckMate 067 and 214 trials for patients with advanced melanoma or renal cell carcinoma (aRCC), respectively, where immunotherapy was often halted for toxicity rather than a predefined treatment endpoint. We therefore sought to assess TFS in the HCRN GU16-260 trial, which was designed to reduce toxicity and cap immunotherapy duration.

Methods: Data were analyzed from 128 patients with clear-cell aRCC treated with first-line nivolumab monotherapy for up to 2 years. Salvage nivolumab/ipilimumab for up to 1 year was provided to eligible patients with disease progression at any point or stable disease at 48 weeks (29% of patients). TFS was defined as the area between Kaplan-Meier curves for a time from registration to protocol therapy cessation and for a time from registration to subsequent systemic therapy initiation or death, estimated from 36-month mean times. The time on or off protocol treatment with grade 3+treatment-related adverse events (TRAEs) was also captured.

Results: At 36 months from enrollment, 68.3% of patients were alive: 96.8% of International Metastatic RCC Database Consortium (IMDC) favorable-risk patients and 56.6% of those with intermediate/poor-risk, respectively. The 36-month mean time on protocol therapy was 11.5 months including 0.6 months with grade 3+TRAEs (16.0 months for favorable-risk patients and 9.6 months for intermediated/poor-risk patients). The 36-month mean TFS for the whole population was 9.4 months (12.9 months including 1.5 months with grade 3+TRAEs for favorable-risk and 8.0 months including 1.0 months with grade 3+TRAEs for intermediate/poor-risk). At 36 months, 65.6% of favorable-risk patients and 27.1% of intermediate/poor-risk patients were alive and subsequent systemic treatment-free.

Conclusions: Nivolumab monotherapy with salvage nivolumab/ipilimumab in non-responders is an active treatment approach in treatment-naïve patients with aRCC and, similar to nivolumab/ipilimumab in CheckMate 214, results in substantial TFS and toxicity-free TFS. TFS was greatest in patients with favorable-risk disease, supporting the use of an immunotherapy-only regimen in this population.