Menstruation span--a time-limited risk factor for endometrial carcinoma.

A case-control study was undertaken to investigate the influence of reproductive factors on the risk of developing endometrial carcinoma. The study comprised 254 women with newly diagnosed endometrial carcinoma, resident in a defined geographical area, and 254 age-matched population controls. Nulliparity and late menopause were positively associated with endometrial carcinoma. Each additional full-term pregnancy resulted in a decrease in the risk by 16%. The importance of parity and menopausal age decreased with increasing life span, and in women older than 69 years these two variables did not discriminate significantly between cases and controls. The calculated number of years of menstruation (the "menstruation span") was used as a combined measure of the impact of parity, age at menarche and age at menopause on the risk of developing endometrial carcinoma. The patients had a significantly longer mean menstruation span than the controls (33.6 versus 31.2 years; p less than 0.001) and a longer span than 39 years gave a 4.2 times higher risk than one shorter than 25 years. It is suggested that the total length of time for which a woman is exposed to unopposed estrogen is important and that the effect of this hormonal influence is time-limited.