Abstract: OBJECTIVE: To investigate the expression of TGF-β1 in congenital cystic adenomatoid malformation of the lung (CCAM) and its role in the formation of CCAM. METHODS： The diseased group included 52 cases of congenital cystoadenomatoid malformation of lung (6 m-15 y)，9 cases of normal lungs (2 m-15 y)and 15 fetal lungs at varying gestational ages (12-39 w) as the control group. Immunohistochemical staining (EliVision) was used to detect the proteins of TGF-β1，hybridization in situ to detect the mRNA of TGF-β1 in every tissue of CCAM，normal pediatric lungs and fetal lungs. RESULTS： The protein of TGF-β1 was mainly expressed in celluar cytoplasm of pulmonary epithelial cells and mesenchymal cells. The expression of TGF-β1 mRNA located in cytoplasm of smooth muscle cells surrounding the bronchus and cysts. The expression level of TGF-β1 and TGF-β1 mRNA in CCAM groups were significantly higher than those in fetal and normal lungs (P<0.05 or P<0.01)，but not significantly different among the diseased groups (P>0.05). CONCLUSION：The overexpression of TGF-β1 may play an important role in the development of congenital cystic adenomatoid malformation，and would warrant our further investigation.

Key words: TGF-β1, congenital cystic adenomatoid malformation of lung, immunohistochemistry, hybridization in situ