Our analysis of publicly available datasets revealed that PTEN is frequently mutated in NSCLC, ranging from transcriptional downregulation to genetic loss, and frequently co-occur with gain of function mutations in the oncogene KRAS and loss of function mutations in the tumor suppressor TP53. PTEN gene dosage is a direct prognostic marker for therapy outcome and patient survival, as already a reduction in gene expression negatively correlated with patient survival and ionizing radiation therapy success for both NSCLC entities, adenocarcinoma and squamous cell carcinoma. The gene discussed is PTEN; the disease is squamous cell carcinoma.