Objective.To investigate PTEN expression and loss of heterozygosity（LOH）of its epigenetic microsatel-lites in gastric carcinoma and explore their roles in tumorigenesis and progression of gastric carcinoma.Methods.LOH of epigenetic microsatellites of PTEN（D10S541

D10S583and D10S1687）was exam-ined in advanced gastric carcinomas（n=56）by PCR-SSCP.The mRNA and protein expressions of PTEN gene were evaluated in normal mucosa（n=56）

early（n=11）and advanced carcinomas（n=56）of the stomach using RT?PCR and immunohistochemoistry respectively.PTEN mRNA and protein expressions were compared with clinicopathological staging and lymph node metastasis of tumors.The relationship be-tween PTEN mRNA expression and LOH of microsatellites was discussed

as well as relationship between PTEN mRNA and protein expression.Results.LOH of D10S541

D10S583and D10S1687was found in28.6%（16/56）of advanced gas-tric carcinomas.The positive rates of PTEN expression were80.4%（45/56）

45.5%（5/11）and32.1%（18/56）in normal gastric mucosa

early and advanced gastric carcinomas at mRNA level

while78.6%（44/56）

36.4%（4/11）and28.6%（16/56）at protein level.PTEN mRNA and protein were less fre-quently expressed in early and advanced gastric carcinomas than normal gastric mucosa（P<0.05）.There was negative correlation between PTEN mRNA expression and LOH of microsatellites（P<0.05）.PTEN protein expression paralleled to its mRNA expression（P<0.05）.The PTEN mRNA and protein expres-sions were negatively correlated with lymph node metastasis of advanced gastric carcinomas（P<0.05）.Conclusion.Down?regulated expression of PTEN and frequent LOH of its epigenetic microsatellites might play an important role in gastric carcinogenesis.Reduced PTEN mRNA expression was closely as-sociated with LOH of its epigenetic microsatellites.Altered expression of PTEN might contribute to lymph node metastasis of gastric carcinoma by decreasing cell adhesion and apoptosis

increasing angiogenesis and cell mobility.