Abstract: OBJECTIVE：To investigate expression of PTEN and PAX-2 in endometrial precancers，and their usefulness as immunohistochemical markers for diagnosis of atypical endometrial hyperplasia (AH). METHODS：Immunohistochemistry was performed to detect PTEN and PAX-2 expressions in 20 cases of AH，25 cases of suspicious atypical endometrial hyperplasia (suspicious AH) ，and 20 cases of endometrial hyperplasia without atypia (EH). RESULTS：When using 10% as the cutoff for weakened or absent PTEN protein expression in epithelial cells，the differences among the three groups were not statistically significant. However，when 75% was used as the cutoff，the differences in expression among the three groups became statistically significant (P<0.01). For PAX-2 protein，when using 10% as the cutoff for weakened or absent nuclear expression in epithelial cells，the difference between the atypical hyperplasia group and the non-atypical hyperplasia group was statistically significant (P=0.000). When 75% was used as the cutoff，the differences in expression among the three groups were statistically significant (P<0.01). Using 75% as the cutoff for weakened or absent expression in epithelial cells，50% of the samples in the atypical hyperplasia group showed overlapping loss of both PTEN and PAX-2 proteins. CONCLUSION：Extensive loss or reduction of PTEN protein expression (>75%) and loss or reduction of PAX-2 protein expression (>10%) may provide diagnostic value for endometrial atypical hyperplasia. The combined loss of both markers，when correlated with HE morphological features，demonstrated higher relevance for diagnosing endometrial atypical hyperplasia.

Key words: atypical endometrial hyperplasia, hyperplasia without atypia, PTEN, PAX-2, immunohisto-chemistry