AIM:To investigate expression of PTEN in gastric cancerand to explore its roles in tumorigenesis and progression ofgastric cancer.METHODS:Formalin-fixed and paraffin-embedded tissuesof adjacent non-tumor mucosa and primary foci from 113cases of gastric cancers were studied for the expressionof PTEN and Caspase-3 and microvessel density (MVD)by streptavidin-peroxidase (S-P) immunohistochemistrywith antibodies against PTEN,Caspase-3,and CD34.Therelationship between PTEN and Caspase 3 expressionand clinicopathological parameters of tumors wascompared.RESULTS:Primary gastric cancer cells expressed PTENless frequently than adjacent epithelial cells of primary foci(54.9 % vs 89.4 %;P=-0.000,χ~2=33.474).PTEN expressionwas significantly associated with invasive depth (P=0.003,rs=0.274),metastasis (P=0.036,rs=0.197),growth pattern(P=0.008,rs=0.282),Lauren’s classification (P=0.000,rs=0.345),and histological classification (P=0.005,rs=0.262)of tumors,but not with tumor size (P=0.639,rs=0.045),Borrmann’s classification (P=0.544,rs=0.070) or TNM staging(P=0.172,rs=0.129).PTEN expression was negativelycorrelated with MDV in primary gastric cancer (P=0.020,F=5.558).Primary gastric cancer cells showed less frequentimmunoreactivity to Caspase-3 than adjacent epithelial cellsof primary loci (32.7 % vs 50.4 %;P=0.007,χ~2=7.286).Caspase-3 expression was dependent of PTEN expression inprimary gastric cancer cells (P=0.000,χ~2=15.266).CONCLUSION: Down-regulated expression of PTEN plays an important role in tumorigenesis, progression, growth,’ differentiation and angiogenesis of gastric cancer. Low expression of PTEN can decrease expression of Caspase-3 to disorder apoptosis of tumor cells, which might explain the molecular mechanisms of PTEN contributions to tumorigenesis and progression of gastric cancer. AIM: To investigate expression of PTEN in gastric cancerand to explore its roles in tumorigenesis and progression of gastric cancer. METHODS: Formalin-fixed and paraffin-embedded tissues of adjacent non-tumor mucosa and primary foci from 113cases of gastric cancers were studied for the expression of PTEN and Caspase-3 and microvessel density (MVD) by streptavidin-peroxidase (SP) immunohistochemistry with antibodies against PTEN, Caspase-3, and CD34. Relationship between PTEN and Caspase 3 expression and clinicopathological parameters of tumors wascompared.RESULTS: Primary gastric cancer cells expressed PTENless (P = 0.003, rs = 0.274), metastasis (P = 0.036, P = 0.003, rs = rs = 0.197), growth pattern (P = 0.008, rs = 0.282), Lauren’s classification (P = 0.000, rs = 0.345), and histological classification (P = 0.005, rs = 0.262) of tumors, but not with tumor size P = 0.639, rs = 0.045), B. orrmann’s classification (P = 0.544, rs = 0.070) or TNM staging (P = 0.172, rs = 0.129) .PTEN expression was negativelycorrelated with MDV in primary gastric cancer (P = 0.0007, χ ~ 2 = 7.286) .Caspase-3 expression was dependent of PTEN expression in primary gastric cancer cells (P = 0.000, χ ~ 2 = 15.266) .CONCLUSION: Down-regulated expression of PTEN plays an important role in tumorigenesis, progression, growth, ’differentiation and angiogenesis of gastric cancer. Low expression of PTEN can decrease expression of Caspase-3 to disorder apoptosis of tumor cells, which might explain the molecular mechanisms of PTEN contributions to tumorigenesis and progression of gastric cancer.