There was also a correlation between increased IEL density and immune checkpoint (PD-1 and PD-L1) expression with disease progression and MSI status, as MSI-H SSLDs and CRCs had significantly higher IEL density values and PD-1/PD-L1 expression compared with MSS-serrated CRCs, supporting the stepwise dysplasia–carcinoma sequence of serrated carcinogenesis and the hypermutator phenotype of MSI-H lesions. This evidence concerns the gene PDCD1 and carcinoma.