PTEN and squamous cell lung carcinoma: Simultaneous loss of PTEN and LKB1 (a tumor suppressor, also known as serine-threonine kinase 11) contributes to the development of murine lung squamous cell carcinoma with higher PD-L1 expression, while PD-L1 in the tumor is not induced by individual deficiency of either PTEN or LKB1 (327).