One of the most closely watched questions in oncology immunotherapy has been whether blocking TIGIT — a second immune checkpoint — on top of PD-L1 inhibition could meaningfully extend survival in lung cancer patients whose tumors express high levels of PD-L1. The SKYSCRAPER-01 results sharpen that answer in a sobering direction for tiragolumab, Roche's lead TIGIT antibody.
The Phase III trial enrolled 521 patients with previously untreated, PD-L1-high (confirmed by the 22C3 assay) locally advanced or metastatic non-small cell lung cancer, randomizing them 1:1 to tiragolumab 600 mg plus atezolizumab 1,200 mg versus placebo plus atezolizumab on 21-day cycles. At the primary progression-free survival analysis in March 2022, the tiragolumab arm showed a median PFS of 7.0 months versus 5.6 months for atezolizumab alone — a statistically nonsignificant result despite a hazard ratio of 0.78 favoring the combination. The final overall survival analysis, with a median follow-up approaching 18 months, produced median OS figures of 23.1 months versus 16.9 months — a numerically meaningful gap that nonetheless failed to cross the prespecified statistical threshold for significance.
These results fit a disheartening pattern for TIGIT inhibition. Earlier Phase II CITYSCAPE data had generated optimism, but Phase III replication has proven elusive across multiple TIGIT programs, including trials with vibostolimab and domvanalimab. The challenge may reflect biological complexity: TIGIT's immunosuppressive role varies considerably by tumor microenvironment composition, and PD-L1 expression alone appears insufficient as a patient-selection biomarker for dual checkpoint benefit. Critically, the control arm performed better than historical baselines suggest, complicating effect detection. For health-conscious adults tracking immunotherapy advances, this trial reinforces that checkpoint combination strategies face steep translational hurdles and that even large, well-designed Phase III trials can fail to validate mechanistically plausible hypotheses. The TIGIT field is not closed, but its near-term therapeutic promise has narrowed considerably.