Abstract: Abstract　Objective: To investigate the expression of L1 in gastrointestinal stromal tumors (GIST)and its significance. Methods: L1 Protein and mRNA were detected in the tissues of 66 cases of GISTs , 10 cases of smooth muscle tumors, 6 cases of schwannoma and 14 cases of the normal bowel by immunohistochemistry and RT-PCR. And the follow up was carry out.The correlation of L1 expression with clinical pathologic features of GIST and the difference L1 expression in between GIST and smooth muscle tumors, schwannoma, the normal bowel tissue were analyzed. Results:　The expression rates of L1 Protein and mRNA in GISTs were 57.6%(38/66) and 83.3% (30/36) , and the difference of the both was significant ( P < 0.05). the expression of L1 had significant difference in different aggressive risk of GIST(P<0.05),but had no correlation with age，sex ,locus, tissue type and survival rate in GIST（P>0.05）. L1 expression in GIST was significant higher than it in smooth muscle tumors and the normal bowel tissue ( P < 0.05) and had no significant difference with it in schwannoma. Conclusion: The expression of L1 may play an important role in tumorigenesis and progression of GIST, which suggest that L1 is applied to diagnosis or differential diagnosis of GIST; Future studies might focus on the impact of the expression of L1on survival.

Key words: gastrointestinal stromal tumors, L1, immunohistochemistry, Reverse transcription polymerase chain reaction