Abstract: The present invention teaches that relatively low levels of serum progesterone, 1 to 6 ng/ml, may be used to prevent endometrial cancer. The vaginal delivery of progesterone using a cross-linked polycarboxylic polymer produces this low serum progesterone level while also providing the full secretory transformation of the endometrium, indicating the efficacy of the progesterone. Such low levels of serum progesterone will decrease the risk of breast cancer experienced by women undergoing hormone replacement therapy ("HRT") and minimize the potential of other undesirable progesterone associated side effects.