Objective To investigate the mutation and expression of tumor suppressor gene-PTEN mRNA and explore their roles in tumorigenesis and progression of ovarian cancer. Methods Mutated exon 5 of PTEN gene was examined in normal ovary（n = 5）

ovarian cyst （n =5）

ovarian borderline tumor （n = 9）

epithelial ovarian cancer（n = 60）

and ovarian cancer cell line （n = 1）by polymerase chain reaction-single strand conformation polymorphism （PCR-SSCP）. mRNA expression of PTEN gene was evaluated in corresponding tissues and cell line by reverse transcription polymerase chain reaction（RT-PCR）. The mutation and mRNA expression of PTEN gene were compared with clini-copathological features of ovarian cancer. Results Mutated exon 5 of PTEN gene was detected only in 5（7.1%）cases of epithelial ovarian cancer. mRNA expression level of PTEN gene in ovarian borderline tumor or ovarian cancer was lower than that in normal ovary or ovarian cyst（P < 0.05）. The level of PTEN gene mRNA expression was negatively correlated with clinicopathological staging of ovarian cancer

whereas positively correlated with histological differentiation （P < 0.05）. mRNA expression level of PTEN gene in ovarian endometrioid cancer was significantly lower than that in ovarian serous or mucinous cancer (P < 0.05=. Conclusions Mutation of PTEN gene occurs in ovarian cancer. Down-regulated expression of PTEN is probably an important molecular event in tumorigenesis of ovarian cancer. Abnormal expression of PTEN gene is involved in progression of ovarian cancer. Reduced expression of PTEN gene is closely associated with tumorigenesis and pathobiological behaviors of ovarian endometrioid cancer.