PTEN and squamous cell lung carcinoma: Clinically, squamous cell lung cancer is characterized by alterations in p53, kelch-like ECH-associated protein 1 (KEAP1), phosphatase and tensin homolog (PTEN)/phosphatidylinositol-3-kinase (PI3K), cyclin dependent kinase inhibitor 2A (CDKN2A), and RB121.