TTF1 and squamous cell carcinoma: Our study also found a significantly higher positive expression rate of TTF-1 in mutant patients, which may be explained by the high positive expression rate of TTF-1 in NSCLC and higher adenocarcinoma rate than squamous cell carcinoma, consistent with the literature (23, 24).The principle of applying PET/CT in lung cancer is based on differences in glucose metabolism between tumor and normal tissues (25).