CHICAGO – (accRCC), according to findings from the phase 2 KEYNOTE-427 study.
At a median follow-up of 12 months, the overall response rate in 110 study participants with at least one post-baseline assessment was 38%. Three patients (2.7%) achieved a complete response and 39 (35.5%) achieved a partial response, David F. McDermott, MD, reported at the annual meeting of the American Society of Clinical Oncology.
“The disease control rate was 59%,” he said.
Overall, 67% of the patients experienced a reduction in tumor burden, 14% experienced at least an 80% reduction, and 7% experienced a 100% reduction of their target lesion, said Dr. McDermott of Beth Israel Deaconess Medical Center, Boston.
“Most tumor responses occurred early in the course of therapy,” he noted.
The median time to response was 2.8 months, and the median duration of response was not reached at data cutoff, but 74.8% of responders had a response lasting at least 6 months.
An analysis by International Metastatic Renal Cell Carcinoma Database Criteria (IMDC) category showed a confirmed overall response rate (ORR) of 32% among 41 patients with favorable risk, and 42% in 69 patients with intermediate or poor risk.
“Nine of 17 patients in the poor risk group achieved a major response,” Dr. McDermott noted. “Complete and durable responders were seen in all IMDC subgroups.”
In 46 patients with increased PD-L1 expression or a combined positive score of at least 1 the confirmed ORR was 50.0%, and in 53 patients with low PD-L1 expression and a combined positive score less than 1 it was 26%. The ORR was 45% in the remaining patients in whom PD-L1testing could not be performed.
“Of note, all of the complete responses were seen in the PD-L1-high or CPS-greater-than-1 group,” he said.
Median progression-free survival was 8.7 months, and median overall survival has not been reached.
Tolerability of pembrolizumab in this study was acceptable and consistent with that seen with pembrolizumab monotherapy in other tumor types. Although 80% of patients experienced a treatment-related adverse event, the events mainly included fatigue, pruritus, diarrhea, rash, and arthralgia, occurring in 12.7% to 27.3% of patients, he said.
Grade 3/4 events occurred in 21.8% of patients and one patient experienced a fatal grade 5 case of pneumonitis, he added, noting that 11% of patients discontinued treatment because of a treatment-related adverse event.
Overall, 61 patients discontinued therapy, and 33 of those discontinued because of disease progression.
Programmed death-1 (PD-1) inhibitor-based combination therapies have been shown to have clinical benefit when used first-line in accRCC, but data with respect to the clinical impact of first-line PD-1 inhibitor monotherapy are lacking, Dr. McDermott explained.
KEYNOTE-427 was a single-arm, open-label, two-cohort study evaluating the efficacy and safety of pembrolizumab as first-line monotherapy in accRCC and advanced non–clear cell RCC (anccRCC). Patients had accRCC or anccRCC, measurable disease, no prior systemic therapy and Karnofsky Performance Status score of 70% or greater. They were treated with intravenous pembrolizumab at a dose of 200 mg every 3 weeks, and response was assessed at week 12, then every 6 weeks thereafter until week 54, then every 12 weeks.
The current analysis focused on the accRCC cohort and showed that in treatment-naive patients with histologically confirmed accRCC and measurable disease, pembrolizumab shows promising antitumor activity across IMDC risk groups, he said.
“Encouraging activity was also observed in key subgroups, such as the IMDC intermediate/poor risk group ... and patients with [programmed death-ligand 1]-positive tumors,” he said. “The findings ... provide support for the exploration of pembrolizumab in the adjuvant setting and will allow investigators to put the benefit of anti-PD-1-based combination therapies in better context,” he concluded, noting that KEYNOTE-564, a study of pembrolizumab in the adjuvant setting is currently enrolling, and the current study (KEYNOTE-427) cohort B exploring pembrolizumab monotherapy in anccRCC patients is ongoing.
Merck sponsored the study. Dr. McDermott reported consulting or advisory roles with Array BioPharma, Bristol-Myers Squibb, Exelixis, Genentech/Roche, Merck, Novartis, Pfizer, and X4 Pharma. His institution has received research funding from Prometheus Laboratories.
SOURCE: McDermott DF et al., ASCO 2018 Abstract 4500.