OBJECTIVE Patients with etoposide/platinum-refractory extensive disease (ED) small-cell lung cancer (SCLC) have a dismal prognosis. We aimed to evaluate the efficacy and safety of pembrolizumab and paclitaxel combination therapy in these patients.

METHODS In this multi-center, phase II study, ED-SCLC patients who showed progression after etoposide/platinum chemotherapy received paclitaxel 175 mg/m² every 3 weeks for up to six cycles. Pembrolizumab 200 mg was added from the second cycle and continued until disease progression or unacceptable toxicity. The primary endpoint was the objective response rate (ORR) and the secondary endpoints were progression-free survival (PFS), overall survival (OS), safety, and biomarker analyses including programmed death-ligand 1 (PD-L1) expression, next-generation sequencing, and flow cytometric analysis of peripheral blood cells.

RESULTS Of the 26 patients enrolled, the confirmed ORR was 23.1% (95%CI: 6.9%-39.3%); complete response: 3.9%, confirmed partial response [PR]: 19.2%, stable disease: 57.7%, progressive disease: 7.7%, and not evaluable: 11.5%. Including 4 cases of unconfirmed PRs, 38.5% of patients were responding and the disease control rate was 80.7%. The median PFS and OS were 5.0 months (95% CI: 2.7-6.7) and 9.1 months (95% CI: 6.5-15.0), respectively. The grade 3 or 4 adverse events observed included febrile neutropenia (7.7%), neutropenia (7.7%), asthenia (7.7%), hyponatremia (7.7%), and type I diabetes (7.7%). Targeted gene sequencing identified no specific genetic alterations correlated with the treatment, except for theMET copy number gain (PFS 10.5 versus 3.4 months, p = 0.019).

CONCLUSIONS Pembrolizumab and paclitaxel combination therapy showed a moderate activity with acceptable toxicity in patients with refractory ED-SCLC.