**7. Long-Term Survival**

A major difference between ICIs and previously reported anticancer drugs is a substantial increase in long-term survival. On pooled analysis of the CheckMate017 and CheckMate057 trials (2019), both of which compared the efficacy of DTX and nivolumab as second-line therapy for NSCLC, the 5-y survival rate of nivolumab was 13.4%; DTX, 2.6% [49]. A 5-y survival rate of > 10% has not yet been achieved using previously reported cytocidal anticancer drugs, and ICIs resulted in a more prolonged long-term survival than conventional anticancer drugs. Furthermore, at 5 y, nivolumab treatment resulted in a response among 32.2% of patients, while no patients responded to DTX.

A follow-up report from the KEYNOTE-001 trial, a phase-I study on pembrolizumab, also reported a 5-y survival rate of 29.6% in the untreated, high PD-L1 group [50]. Notwithstanding a high long-term survival rate, the expression of PD-L1 and the frequency of TMBs are considered suitable predictors. Rizvi et al. reported that 62 patients with NSCLC, who received an ICI and acquired a PFS of ≥18 mo, presented significantly better outcomes on the basis of both PD-L1 and TMB in comparison with untreated patients (rate of PD-L1 TPS ≥ 50%: 43% vs. 23% TMB: 12.24 vs. 6.34 Mut/Mb) [51].

Though not observed in a majority of patients, treatment with immune checkpoint inhibitors may result in long-term survival, and establishment of biomarkers on long-term surviving cases is desirable.
