In contrast to the high incidence of endometrial neoplasm (~27%) and atypical hyperplasia (40%) associated with PTEN heterozygotic deficiency8, 9, 21, 32, the expression of mfat-1 in the PTEN+/− mice displayed no malignant endometrial lesion and significantly reduced incidence of atypical complex hyperplasia (30%). This evidence concerns the gene PTEN and endometrial neoplasm.