PDCD1 and cancer: The GSEA analysis (minGSSize = 50, maxGSSize = 500) of the DEGs was obtained by the comparison of the sun-exposed and unexposed groups in subcluster 1 and showed 8 activated pathways including T-cell receptor signaling pathways, PD-L1 expression, and PD-1 checkpoint pathways in cancer (Figure 6c), which may indicate the relationship between photoaging and PD-1-PD-L1 pathway.