Median overall survival in the intent-to-treat population was 14.2 months with atezolizumab versus 13.5 months without it (HR, 0.88). Patients with high PD-L1 expression (14% and 13% of patients in the groups, respectively), experienced dramatic, clinically important improvement in overall survival with atezolizumab plus chemotherapy, compared with chemotherapy alone (median of 23.4 vs. 10.2 months; HR, 0.48).
In IMpower 131, PD-L1-high expression was defined as TC3 or IC3 – expression on greater than 50% of tumor cells or greater than 10% of immune cells. Patients were also categorized as PD-L1 positive (TC 1/2/3 or IC 1/2/3 – expression of PD-L1 on 1% or greater of tumor cells or immune cells) or PD-LI negative (TC 0 or IC 0 – expression on less than 1% of cells). The PD-L1-positive and negative subsets did not demonstrate improved overall survival with atezolizumab.
How these results influence clinical practice
As noted above, in NSCLC patients (regardless of histology), we need biomarkers that predict benefit from ICIs alone and additive benefit when ICIs are combined with other, potentially toxic therapies. In the subset analysis of IMpower 131, despite clinically relevant differences in overall survival for the “PD-L1-high” patients, the PD-L1-positive patients did not benefit, so PD-L1 tumor proportion score remains an imperfect biomarker.
To put this report in its proper context, it will be important to analyze the details of the final manuscript of IMpower 131, particularly the comparison of arms A plus B versus C and the proportion of arm C patients who ultimately received an ICI in the second- or later-line setting. In the meantime, clinicians will select their ICI and chemotherapy regimen of choice, utilizing PD-L1 expression as an “eyebrow raiser,” but not an exclusionary criteria – as they did prior to WCLC 2019.
Dr. Lyss has been a community-based medical oncologist and clinical researcher for more than 35 years, practicing in St. Louis. His clinical and research interests are in the prevention, diagnosis, and treatment of breast and lung cancers and in expanding access to clinical trials to medically underserved populations.