A combination of the tyrosine kinase inhibitor axitinib (Inlyta) and the immune checkpoint inhibitor pembrolizumab (Keytruda) was associated with acceptable toxicities and showed promising activity against advanced renal cell carcinoma (RCC) in the first-line setting, results of a phase 1b trial indicate.
Of 11 patients enrolled in a dose-finding study and 41 enrolled in the expansion phase of that study, 38 had an objective response (complete or partial response), for an overall response rate of 73%, reported Michael B. Atkins, MD, of Georgetown-Lombardi Comprehensive Cancer Center, Washington, and his colleagues.
“This phase 1b study showed that the combination of axitinib and pembrolizumab at nearly the full planned doses of each drug is tolerable in patients with treatment-naive advanced renal cell carcinoma,” they wrote. The report was published in.
Previous studies of programmed death-1 (PD-1) checkpoint inhibitors such as pembrolizumab or nivolumab (Opdivo) combined with inhibitors of vascular endothelial growth factor (VEGF) have resulted in excessive toxicities attributed to off-target effects of the VEGF inhibitors used.
The investigators reasoned that because axitinib is more selective and specific for targets in the VEGF pathway, it might make a safer and more effective partner to a PD-1 inhibitor than the multikinase inhibitors sunitinib (Sutent) or pazopanib (Votrient).
“A formal systematic review was not done before doing this trial because most of the work combining VEGF pathway inhibitors with checkpoint inhibitors is new and not yet published,” Dr. Atkins and his associates explained.
As of the March 31, 2017, data cutoff, 52 patients from 10 U.S. centers had been treated with the same dose and schedule and were included in the analysis. All patients had tumors with clear cell renal carcinoma histologies; one also had sarcomatoid features.
There were three investigator-assessed dose-limiting toxicities (DLT, the primary endpoint) in the 11 patients treated in the dose-finding phase. One of the patients had a transient ischemic attack and two completed less than 75% of the planned axitinib dose because of treatment-related toxicities.
Of the 52 patients, 25 were still on treatment at the time of data cutoff: 22 who were still receiving both axitinib and pembrolizumab and 3 who were receiving only the PD-1 inhibitor. Eight of the patients continued on therapy despite disease progression.
Of the 27 patients who discontinued both drugs, 10 did so because of adverse events, 9 for disease progression, and others for various reasons such as mixed adverse events and disease progression, investigator discretion, global deterioration, or protocol violation.
Grade 3 or greater adverse events occurred in 34 patients (65%), and included hypertension, diarrhea, fatigue, and elevated alanine aminostransferase (ALT) levels.
The most common potentially immune-related adverse events were diarrhea, ALT elevations, hypothyroidism, and fatigue.
At a median follow-up of 20.4 months, 4 patients had a complete response, and 34 had a partial response. An additional eight patients had stable disease. Responses were seen in 18 of 24 patients with favorable-risk disease and in 18 of 26 patients with intermediate- or poor-risk disease. The median time to response was 2.8 months, and the median duration of response was 18.6 months. “Future research should focus on investigating the mechanism of the potential synergistic effects of axitinib and pembrolizumab, and whether an immunotherapy-only approach (including combinations) enriched by the appropriate biomarkers, followed by VEGFR TKI salvage, might produce more durable off-treatment responses or whether administering VEGFR TKI monotherapy followed by PD-1 and PD-L1 pathway blockade might produce superior or equivalent results,” the investigators concluded.
Pfizer, in collaboration with Merck, sponsored the study. Dr. Atkins and several coauthors disclosed consulting fees from Pfizer, Merck, and other companies. Four of the coauthors are Pfizer employees and stockholders.
SOURCE: Atkins MB et al. Lancet Oncol 2018 Feb. 10. .