Endometrial cancer is a disease of the affluent, developed world, where epidemiological studies have shown that > or =40% of its incidence can be attributed to excess
body weight. An additional proportion may be because of lack of physical activity. Alterations in endogenous
hormone metabolism may provide the main links between
endometrial cancer risk, and excess
body weight and physical inactivity. Epidemiological studies have shown increased
endometrial cancer risks among pre- and postmenopausal women who have elevated plasma
androstenedione and
testosterone, and among postmenopausal women who have increased levels of
estrone and
estradiol. Furthermore, there is evidence that chronic
hyperinsulinemia is a risk factor. These relationships can all be interpreted in the light of the "unopposed
estrogen" hypothesis, which proposes that
endometrial cancer may develop as a result of the mitogenic effects of
estrogens, when these are insufficiently counterbalanced by
progesterone. In our overall synthesis, we conclude that development of ovarian
hyperandrogenism may be a central mechanism relating nutritional lifestyle factors to
endometrial cancer risk. In premenopausal women, ovarian
hyperandrogenism likely increases risk by inducing chronic
anovulation and
progesterone deficiency. After the menopause, when
progesterone synthesis has ceased altogether, excess weight may continue increasing risk through elevated plasma levels of
androgen precursors, increasing
estrogen levels through the aromatization of the
androgens in adipose tissue. The ovarian
androgen excess may be because of an interaction between
obesity-related, chronic
hyperinsulinemia with genetic factors predisposing to the development of ovarian
hyperandrogenism.