IMpower133

The double-blind, placebo-controlled, Phase III IMpower133 (NCT02763579) trial randomly assigned 403 extensive-stage SCLC patients 1:1 to either receive four cycles of atezolizumab plus carboplatin and etoposide (N=201) or four cycles of placebo plus carboplatin and etoposide (N=202). Both arms were followed by maintenance atezolizumab or placebo according to the initial assignment. Treatment continued until unacceptable toxicities, disease progression (RECIST 1.1), or no additional clinical benefit. The composite primary endpoint included investigator-assessed PFS and OS in the intention-to-treat (ITT) population.

At median follow-up of 13.9 months, the median OS measured 12.3 months for the combination atezolizumab plus chemotherapy vs 10.3 months for placebo plus chemotherapy (HR=0.70; 95% CI, 0.54-0.91; p=0.007). The median PFS were 5.2 months and 4.3 months, respectively (HR=0.77; 95% CI, 0.62-0.96; p=0.02).

The authors reported that the safety of atezolizumab plus carboplatin and etoposide appeared consistent with the previously reported safety profile of each of the individual agents alone. No new safety signals were observed.