PDCD1 and neoplasm: The date of staining confirmation of this tissue was 28 to 31 days after tumor cell inoculation, since the peak of PD-L1 expression in PD-1 antibody therapy to tumor-bearing mouse in vivo has been reported in the literature to come relatively early, around 9 days after tumor cell inoculation [36], and then expression may have decreased due to tumor resistance mechanisms.