There can be no doubt that oestrogen can alter the behaviour of this tumour but there is still a question about oestrogen as a primary causal agent Approximately 75%of cases of endometrial cancer occur in the postmenopausal period when estrogen values are low and progesterone is absent. Nulliparity and Pco syndrome(with defective progesterone synthesis ) carry an increased risk 2003-10-27 Carcinoma of the endometrium 52003-10-27 Carcinoma of the Endometrium 5 There can be no doubt that oestrogen can alter the behaviour of this tumour but there is still a question about oestrogen as a primary causal agent． Approximately 75％of cases of endometrial cancer occur in the postmenopausal period when estrogen values are low and progesterone is absent．Nulliparity and PCO syndrome（with defective progesterone synthesis）carry an increased risk．