These results raise the question of whether learn more metformin also has a beneficial effect on the endometrium in women with PCOS and EC. A recent study from our laboratory has shown that a combination of metformin and oral contraceptives is capable of reverting early-stage EC into normal endometria in addition to improving insulin resistance in women with PCOS [49]. Although this is a promising result, we note that our preliminary report must be taken with caution and that further research is certainly needed before co-treatment with metformin and oral contraceptives can be recommended in clinical practice. Having said that, the promising results with metformin raise the questions

of whether metformin alone affects endometrial function in women with PCOS, how a positive effect of metformin combined with oral contraceptives could inhibit the development of atypical endometrial Stem Cells inhibitor find more hyperplasia and EC at the molecular level, how our findings

affect treatment guidelines for PCOS women with and without insulin resistance, whether metformin as a general anti-cancer drug inhibits EC development in women regardless of whether they also have PCOS, and whether metformin can prevent EC development in women without endometrial pathology but only with risk factors or in women with pre-malignant endometrial disease. Promising evidence for the use of metformin in women with EC It is still far too early to say whether there is any future for metformin as a means of preventing or treating EC in women, and there are no clinical trials assessing single metformin treatment of recurrent or metastatic

EC. However, metformin, in combination with mammalian target of rapamycin (mTOR) inhibitors, seems to be effective in inhibiting EC progression in women with recurrent or metastatic EC [67] and it is also associated with improved recurrence-free survival and overall survival in postmenopausal ADAMTS5 women with diabetes mellitus and EC [34]. Possible mechanisms of metformin in the endometrium Expression and localization of OCTs and MATEs Metformin is highly hydrophilic and readily crosses the plasma membrane [68]. However, there is convincing evidence that organic cation transporters (OCTs) are actively involved in the cellular uptake of metformin and that multidrug and toxin extrusion proteins (MATEs) contribute to the excretion of metformin [69]. Although OCT1–3 and MATE1 and 2 have been identified in humans and rodents [69] – and although OCTs and MATEs are often co-localized in vivo [70] – the actual distributions of OCT1–3 and MATE1 and 2 have been shown to be species and tissue specific [69, 70]. The human endometrium, the specialized lining of the uterus, is composed mainly of luminal and glandular epithelial cells along with fibroblastic cells that make up the stroma [71].