Treatment rationale and design of the PROLONG study: safety and efficacy of pembrolizumab as first-line therapy for elderly patients with non-small cell lung cancer

Phase 2 study of first-line pembrolizumab monotherapy in elderly patients with non-small-cell lung cancer expressing high PD-L1

Background

Pembrolizumab is the recommended first‐line therapy for patients with advanced non‐small‐cell lung cancer (NSCLC) and a programmed death ligand‐1 (PD‐L1) tumor proportion score (TPS) of ≥50% without driver mutations. However, its efficacy and safety for patients ≥75 years have not been prospectively investigated; this was the aim of this study.

Methods

This multicenter and open‐label single‐arm phase II study was conducted at 12 institutions. Chemotherapy‐naïve patients with advanced NSCLC and a PD‐L1 TPS of ≥50% without EGFR mutations or translocation of the ALK received pembrolizumab every 3 weeks. The primary endpoint was progression‐free survival (PFS) with a threshold of 4.3 months. The secondary endpoints were overall survival (OS), objective response rate (ORR), disease control rate (DCR), safety, and quality of life.

Results

Twenty‐six patients were enrolled between October 2017 and March 2020. The median PFS was 9.6 (95% confidence interval [CI] 2.1–20.6) months. The lower limit of the 95% CI did not exceed the target. The median OS was 21.6 months. The ORR and DCR were 41.7% and 70.8%, respectively. The proportion of patients with grade ≥3 treatment‐related adverse events was 15.4%. The quality of life score did not change significantly during treatment.

Conclusion

While this study showed that pembrolizumab was a tolerable treatment for elderly patients, the safety requires further confirmation in a larger study. Although the primary endpoint, the median PFS (9.6 months), was slightly shorter than that (10.3 months) of the previous phase III study (KEYNOTE‐024 study), the median PFS did not achieve the expected value.

Ongoing challenges of using immunotherapy in special populations: Poor performance status patients, elderly patients, and people living with HIV

Immunotherapy with immune checkpoint inhibitors (ICIs) represents a breakthrough in lung cancer treatment. The efficacy of monoclonal antibodies targeting the programmed cell death protein 1 (PD-1), its ligand L1 (PD-L1), and cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4) pathways has been demonstrated in several randomized trials, resulting in significantly improved survival rates in lung cancer patients, especially those with non-small-cell lung cancer (NSCLC), compared to standard chemotherapy. Hence, new therapeutic options have been opened up for advanced-stage lung cancer patients. However, most clinical trials on ICIs conducted so far have either excluded patients with poor performance status (PS) or chronic infections like human immunodeficiency virus (HIV), or accrued only a minor proportion of elderly patients despite the lack of an upper age limit. Our review paper provides a brief summary on the ICI data obtained so far in these special populations. Further dedicated studies are urgently needed to enable us to draw definitive conclusions on the usefulness of ICI in these special patient populations. The combination of ICI and chemotherapy must also be further assessed. It would, additionally, be useful to determine reliable biomarkers that should help us identify those patients who are more likely to benefit from ICI therapy.