Peripheral NK cells identified as the predictor of response in extensive-stage small cell lung cancer patients treated with first-line immunotherapy plus chemotherapy.

PURPOSE: Although immunotherapy improves outcomes in extensive-stage small-cell lung cancer (ES-SCLC), the search for biomarkers predicting treatment success is crucial. Natural killer (NK) cells are potential indicators in various cancers, however, their precise role in ES-SCLC prognosis remains unclear.

METHODS: In this retrospective study, 33 patients with ES-SCLC treated with first-line immuno-chemotherapy were enrolled. The peripheral NK cell percentage and its longitudinal dynamics were analyzed using flow cytometry. Progression-free survival (PFS) and overall survival (OS) were calculated as hazard ratio (HR) and compared statistically.

RESULTS: The median PFS was better in the group with normal baseline NK cell levels than the low group (7.0 vs. 4.6 months; HR = 0.17; 95% CI 0.07-0.41; P < 0.0001), but there was no association with OS (14.9 vs. 10.3 months; HR = 0.55; 95% CI 0.23-1.31; P = 0.171). Furthermore, the NK cell% for 95.0% of patients increased after immunochemotherapy in the clinical response group (P = 0.0047), which led to a better median PFS (6.3 vs. 2.1 months; HR = 0.23; 95% CI 0.05-0.98; P < 0.0001) and OS (14.9 vs. 5.9 months; HR = 0.20; 95% CI 0.04-1.02; P < 0.0001). Similar trends were observed with NK cell% changes up to disease progression, improving PFS (6.5 vs. 4.3; HR = 0.41; 95% CI 0.12-0.92; P = 0.0049) and OS (17.4 vs. 9.7; HR = 0.42; 95% CI 0.17-1.02; P < 0.0001).

CONCLUSION: In patients with ES-SCLC, the percentage and changes in peripheral NK cells can predict the response to combined immunotherapy and chemotherapy.