PDCD1 and neoplasm: Regarding the HPD mice (with an incidence of approximately 9.2% [11/119]), defined accordingly, based on tumor volumes >600 mm3, the average tumor volume was 669 mm3, as shown in Figure 5A. These results suggested that primary resistance and HPD to treatment with the first-line anti-PD-1 antibody remains a challenging issue in cancer immunotherapy.