[ ABSTRACT] AIM: To explore the relationship between FRAS 1 protein and brain metastases of non-small cell lung cancer (NSCLC).METHODS:The mRNA expression of FRAS1 in the brain metastatic tumor tissues and primary tumor tissues of NSCLC was detected by qPCR .The protein expression of FRAS 1 in the tumor tissues and normal tissues adjacent to tumor tissues of NSCLC was measured by SP method of immunohistochemistry .The protein expression of FRAS 1 in NSCLC primary tumor tissues with or without brain metastases was also determined .RESULTS:The mRNA expression of FRAS1 in the brain metastatic zone was nearly 10 times higher than that in the primary tumor tissues , and there was sig-nificant difference between the 2 groups (P<0.05).FRAS1 protein was expressed in the NSCLC primary tumor tissues , but was not found in the normal tissues adjacent to primary tumor tissues .The protein expression of FRAS 1 in the NSCLC with brain metastases was significantly higher than that without brain metastases ( P<0.01 ) .CONCLUSION: FRAS1 protein may be associated with the occurrence of NSCLC .The over-expression of FRAS1 protein may be related to brain metastases with NSCLC .