Aim: To explore the value of rate of cancer progression (ROP) prior to starting PD-1 inhibitors as a predictive and prognostic biomarker. Materials methods: Retrospective data of patients with metastatic non-small-cell lung cancer treated with second-line PD-1 inhibitors were collected. Patients were divided into two groups: slow and rapid based on their ROP. Results: A total of 73 patients were eligible. Progression-free survival (PFS) was significantly shorter in rapid ROP, compared with slow (1.7 vs 4.8 months; HR: 2.42; 95% CI: 1.36-4.30; p = 0.008), as was the overall survival (OS; 5.6 vs 18.7 months; HR: 2.30; 95% CI: 1.13-4.69; p = 0.02). Overall response rate (40 vs 17%) was numerically higher in slow ROP than rapid (p = 0.19). PFS/OS did not correlate with the best response to their last chemotherapy or time to progression from previous line of therapy. Presence of a targetable mutation negatively correlated with PFS/OS. Conclusion: ROP prior to starting PD-1 inhibitors correlates with survival. PFS/OS were shorter in rapid ROP.