PTEN is a tumor suppressor gene mapped on chromosome 10q23.3 and encodes a dual specificity phosphatase. PTEN has major implication in PI3 kinase (PI3K) signal transduction pathway and negatively controls PI3 phosphorylation. It has been reported to be implicated in cell cycle progression and cell death control through inhibition of PI3K-Akt signal transduction pathway and in the control of cell migration and spreading through its interaction with focal adhesion kinase. Somatic mutations of PTEN are frequently detected in several cancer types including brain, prostate and endometrium with more than 30% of tumor tissue specimens bearing PTEN mutations and/or deletions. Because of its high frequency of mutations and its important function as tumor suppressor gene, PTEN is a good candidate for gene therapy. Inducible expression of PTEN has been also reported. In cancer cells bearing PTEN abnormalities, the reversion of PTEN function by external gene transfer becomes more and more investigated in cancer treatment research. Several technologies including the photochemical internalization (PCI) and aiming at improving the transfection efficiency have been reported. PCI is an innovative procedure based on light-induced delivery of macromolecules such as DNA, proteins and other therapeutic molecules from endocytic vesicles to the cytosol of target cells. PCI has been reported to enhance the gene delivery potential of viral and nonviral vectors. The present study was designed to evaluate the influence of photochemical internalization on polyethylenimine (PEI)-mediated PTEN gene transfer and its effects on the cellular viability in Ishikawa endometrial cancer cells bearing PTEN abnormalities. PCI was found to significantly (P < 0.01) enhance PTEN mRNA expression (4.2 fold increase). Subsequently, following PEI-mediated PTEN gene transfer, the restoration of the PTEN protein expression was observed. As a consequence, significant cell growth inhibition (44%) was observed in Ishikawa endometrial cells. Using PCI for PEI-mediated PTEN gene transfer was found to further enhance PTEN mRNA and protein expression as well as PTEN-related cell growth inhibition reaching 89%.