The APOE expression level was statistically significantly lower in certain tumor tissues than in the matched control tissues, particularly in cholangiocarcinoma (CHOL), with a p-value less than 0.001), and Colon adenocarcinoma (COAD), PAAD, Ovarian serous cystadenocarcinoma (OVs), and Pheochromocytoma and Paraganglioma (PCPG), all with p < 0.01. Here, APOE is linked to pheochromocytoma-paraganglioma.