PDCD1 and neoplasm: However, interestingly, probiotic supplementation synergized the antitumor effect of anti-PD-1 treatment (mean tumor size ± SEM of CT and MC groups = 538.63 ± 24.03 and 807.29 ± 24.03 mm3 at day 14, P = 0.014; 1,087.22 ± 53.67 and 1,371.28 ± 47.01 mm3 at day 18, P = 0.258; 1,681.02 ± 77.86 and 2,511.05 ± 83.64 mm3 at day 24, P = 0.014), indicating that the synergistic effect was seen as early as 4 days after the first anti-PD-1 antibody injection (Figure 1B).