PTEN and colorectal cancer: Loss of PTEN (a tumor suppressor that negatively regulates PI3K-AKT-mTOR signaling) or mutations in PIK3CA (a catalytic subunit of PI3K) leads to elevated PD-L1 expression via constitutive PI3K-ATK-mTOR pathway activation in squamous cell lung carcinoma (132, 133), NSCLC (130), gliomas (134), colorectal cancer (135), prostate cancer (136), and breast cancer (137).