ALK and squamous cell lung carcinoma: Previous retrospective literature indicated that ALK positiveness is more common in young and never smoking or light smoking NSCLC patients [30], and ALK fusion gene mainly occurs in lung adenocarcinoma, which is extremely rare in lung squamous cell carcinoma or other histological types of NSCLC [31] [32].The results of our study are consistent with the above conclusions: the proportion of young, adenocarcinoma and never smoking patients is significantly higher, which reflects the specific population distribution characteristics of ALK fusion gene mutation.