APOC1 and esophageal squamous cell carcinoma: GO functional annotation analysis revealed that APOC1 co-expressed genes in ESCC were mainly involved in the following aspects: regulation of T cell activation, cornification, cytolysis, external side of plasma membrane, MHC protein complex, MHC class II protein complex, serine−type peptidase activity, serine-type endopeptidase activity (Supplementary Table S1; Figure 5A).