OBJECTIVES: PTPN13 is a new candidate tumor-suppressing gene. To investigate the 
PTPN13 expression and its potential function in the invasion and metastasis of 
lung squamous cell carcinoma (LSCC), we performed this study in 91 primary LSCC 
tissues and the adjacent non-cancerous tissues.
METHODS: The mRNA expression of PTPN13 and FAK was quantitated by reverse 
transcription polymerase chain reaction. The protein expression of PTPN13, focal 
adhesion kinase (FAK) and phosphorylated FAK (P-FAK) was evaluated using 
immunohistochemical staining and western blotting. The association among PTPN13 
expression, FAK expression and the clinicopathological parameters were analyzed.
RESULTS: PTPN13 expression was down-regulated in LSCC, and was negatively 
correlated with the cancer grade and stage. FAK mRNA, as well as FAK protein 
level was elevated in LSCC tissues. P-FAK level, also found increased, had no 
association with FAK mRNA and FAK protein expression, but had a negative 
correlation with the PTPN13 expression. P-FAK level had a significant positive 
correlation with the TNM classification.
CONCLUSION: The over-expression of FAK and increased FAK phosphorylation plays 
an important role in the invasion and metastasis of LSCC.