Patients who received tiragolumab, an anti-TIGIT antibody, in combination with atezolizumab, a PD-L1 inhibitor, had superior overall response rates (ORR) and progression-free survival (PFS), when compared with results of patients who received placebo with atezolizumab.
Melissa L. Johnson, MD, of the Sarah Cannon Research Institute in Nashville, Tenn., presented these results as part of the American Society of Clinical Oncology virtual scientific program.
Dr. Johnson explained that TIGIT is an immunomodulatory receptor present on activated T cells and natural killer cells in multiple cancers, including NSCLC.
“TIGIT inhibits T cells and natural killer cells by binding to its ligand PVR on tumor cells and antigen-presenting cells,” she said. “TIGIT expression strongly correlates with PD-1 expression, sometimes on the same tumor-infiltrating T cells in lung cancer. So the hypothesis of this trial was that anti-TIGIT antibodies, which prevent TIGIT from binding to its ligand, could restore the antitumor response and could complement the activity of anti–PD-L1/PD-1 antibodies.”
Dr. Johnson noted that combination anti–TIGIT/PD-L1 antibody treatment synergistically improved tumor control and prolonged survival over either antibody alone in preclinical models (Cancer Cell. 2014 Dec 8;26[6]:923-937). In addition, tiragolumab has been evaluated in a phase 1 study, both as monotherapy and in combination with atezolizumab, in multiple solid tumors (NCT02794571).
The phase 2 CITYSCAPE study (NCT03563716) was initiated to confirm the efficacy and safety of tiragolumab plus atezolizumab versus placebo plus atezolizumab for the first-line treatment of NSCLC, Dr. Johnson said.
CITYSCAPE enrolled 135 patients with chemotherapy-naive, PD-L1–positive, locally advanced or metastatic NSCLC. Patients did not have EGFR or ALK alterations.
Half of patients (n = 68) were randomized to receive tiragolumab at 600 mg plus atezolizumab at 1,200 mg, both given on day 1 of every 3-week cycle. The other half of patients (n = 67) were randomized to receive atezolizumab at the same dose and schedule plus placebo.
ORR and PFS
The study’s primary analysis was conducted in June 2019 at a median follow-up of 5.9 months. At that time, the ORR and PFS data showed an early benefit with tiragolumab. The ORR was 31% in the tiragolumab arm and 16% in the placebo arm. The median PFS was 5.42 months and 3.58 months, respectively (hazard ratio, 0.57).
With an additional 6 months of follow-up, the tiragolumab benefit persisted, Dr. Johnson said. The updated ORR in the intent-to-treat population was 37% in the tiragolumab arm and 21% in the placebo arm. The median PFS was 5.6 months and 3.9 months, respectively (HR, 0.58).
The tiragolumab combination showed “clinically meaningful” improvements in ORR and PFS, Dr. Johnson said. She also noted “a greater magnitude of improvement” was seen in patients with a PD-L1 tumor proportion score of 50% or greater.
There were 29 patients in each treatment arm with a PD-L1 tumor proportion score of 50% or greater. Among these patients, the ORR was 66% in the tiragolumab arm and 24% in the placebo arm. The median PFS was not reached and 4.1 months, respectively (HR, 0.30).
There were no significant differences in ORR or PFS among patients with PD-L1 tumor proportion scores below 50%, Dr. Johnson noted.
She added that duration of response and overall survival data are not yet mature and will be presented at a future conference.