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Adding pembrolizumab to first-line etoposide-platinum (EP) chemotherapy can provide “clinically meaningful” improvements in survival for patients with extensive-stage small cell lung cancer (ES-SCLC), according to a presentation at the IASLC 2022 World Conference on Lung Cancer.
Updated phase 3 data showed a 3-fold improvement in overall survival (OS) rate and a 14-fold improvement in progression-free survival (PFS) rate when pembrolizumab was added to EP.
These results, from the KEYNOTE-604 study (ClinicalTrials.gov Identifier: NCT03066778), were presented by Charles M. Rudin, MD, PhD, of Memorial Sloan Kettering Cancer Center in New York, New York.
The trial included 453 patients with ES-SCLC who had received no prior systemic therapy. They were randomly assigned to receive pembrolizumab at 200 mg on day 1 plus EP (n=228) or placebo plus EP (n=225). EP consisted of etoposide (100 mg/m2 on days 1-3) and either carboplatin (AUC5 on day 1) or cisplatin (75 mg/m2 on day 1).
Patients received combination treatment every 3 weeks for 4 cycles. Patients in the pembrolizumab arm could continue on with pembrolizumab (200 mg on day 1 every 3 weeks) for up to 31 additional cycles. Patients in either arm could receive prophylactic cranial irradiation as well.
Nearly all patients — 92% in the pembrolizumab arm and 99.1% in the placebo arm — discontinued study treatment, most due to progressive disease. A majority of patients — 54.7% and 66.8%, respectively — received subsequent therapy.
The median follow-up was 43.3 months. The median OS was 10.8 months in the pembrolizumab arm and 9.7 months in the placebo arm (HR, 0.76; 95% CI, 0.63-0.93). The 3-year OS rates were 15.5% and 5.9%, respectively.
The median PFS was 4.8 months in the pembrolizumab arm and 4.3 months in the placebo arm (HR, 0.70; 95% CI, 0.57-0.85). The 3-year PFS rates were 6.9% and 0.5%, respectively.
The overall response rate was 70.6% in the pembrolizumab arm and 61.8% in the placebo arm. The median duration of response was 4.2 months and 3.7 months, respectively.
For patients who completed 35 cycles of pembrolizumab, the overall response rate was 100%, the median duration of response was not reached, and the 2-year OS rate was 72.2%.
There were 18 patients who completed 35 cycles of pembrolizumab, and 14 of these patients were still alive at last follow-up and no longer receiving chemotherapy or immunotherapy, Dr Rudin noted. The same is true for 2 patients in the control arm.
Overall, grade 3-5 adverse events were observed in 78.9% of patients in the pembrolizumab arm and 77.1% of those in the placebo arm. Treatment-related fatal adverse events occurred in 2.7% of patients in each arm.
Dr Rudin concluded that pembrolizumab plus EP showed “clinically meaningful” improvements over placebo plus EP at about 3.5 years of follow-up.
“I think these results support the continued exploration of pembrolizumab-based combinations for the treatment of small cell lung cancer,” Dr Rudin said.