Objective To investigate the expression of PTEN and Caspase-3 in malignant lymphoma of the stomach and explore their role in progression of primary gastric malignant lymphoma. Methods Formalin-fixed paraffin embedded tissues from 56 cases of primary gastric malignant lymphoma and their adjacent non-tumor mucosa were evaluated for PTEN and Caspase-3 protein ex-pression by streptavidin-biotin-complex （SABC） immunohistochemistry. Their expression was compared with clinical tumor parameters with the relationship between PTEN and Caspase-3 expression concerned as well. Results The positive rate of PTEN expression in primary gastric lymphomas（50.0%

28/56） was significantly lower than that in adjacent non-tumor gastric mucosa（96.4%

27/28）（P < 0.05）. Meanwhile

43 of 56（76.8%）gastric lymphomas indicated Caspase-3 expression

less than that in adjacent non-tumor mucosa （93.5%

29/31） （P < 0.05）. The expression of PTEN was negatively correlated with invasion and lymph node metastasis of gastric lymphoma（P < 0.05）

while the Caspase-3 expression was negatively associated with the latter one（P < 0.05）. Additionally

the PTEN expression was posi-tively correlated with Caspase-3 expression in the primary gastric malignant lymphoma（P < 0.05）. Conclusions The down-regulated expression of PTEN and Caspase-3 played an important role in progression of primary malignant gastric lymphoma. PTEN

as a molecular marker of pathobiological behaviors of tumor

contributes to tumor progression by increasing cell mobility and angiogenesis

as well as decreasing cell adhesion and apoptosis.