CD8A and neoplasm: In conclusion, our observation revealed the following characteristics of the immune microenvironment in PPGL: 1) PPGL is a microsatellite stable tumor with low TMB levels, weak neoantigen production, and poor tumor antigenicity; 2) Due to the low positive rates and low levels, PD-L1 expression is not associated with the degree of tumor malignancy; 3) The number of intratumoral infiltrating CD4+ and CD8+ lymphocytes is low.