Compared with PD-1 inhibitor (nivolumab) or CTLA-4 inhibitor (ipilimumab) monotherapy, PD-1 inhibitor and CTLA-4 inhibitor (nivolumab plus ipilimumab) combination therapies showed significant increase in grade 1-5 and grade 3-5 pneumonitis (RR 3.47, 95%CI:1.76-6.83, p < 0.001; RR 3.48, 95%CI:1.10-11.02, p < 0.001) (Figure 1), but not in pneumonia (Figure 2). Here, CTLA4 is linked to pneumonitis.