Menstrual and reproductive factors in relation to risk of endometrial cancer in Chinese women

Abstract

Menstrual, reproductive and contraceptive factors have been associated with risk of endometrial cancer in populations where the incidence of this tumor is high. To investigate associations between these factors in a low-risk population with a low prevalence of hormone replacement therapy, we conducted a cohort study among 267,400 women employed in the textile industry in Shanghai, China. Menstrual, reproductive and other factors were ascertained at baseline in 1989-1991, and women were followed for incident endometrial cancer through 31 December 1998 (n = 206). Cox proportional hazards modeling was used to estimate hazard ratios (HR) and 95% confidence intervals (CI). Risk of endometrial cancer decreased with increasing age at menarche (p-trend = 0.004). Among menopausal women, risk increased with age at menopause and increasing years of menstruation. Compared to women with one live birth, risk was increased in relation to nulliparity (Hazard ratio = 3.95, 95% CI 1.43-10.86). Risk was decreased with increasing age at first live birth (p-trend = 0.03). There was a decreased risk associated with ever use of an intrauterine device (HR = 0.56, 95% CI 0.35-0.88) and use of oral contraceptives for > or =2 years (HR = 0.50, 95% CI 0.23-1.07). This prospective study confirms findings from previous case-control studies relating menstrual, reproductive, and contraceptive factors and endometrial carcinoma.

Reproductive risk factors for endometrial cancer among Polish women

“…Our investigation also enabled evaluation of effects of shortterm pregnancies, including spontaneous and induced abortions. Although several studies have noted either reduced (Parazzini et al, 1998;Parslov et al, 2000) or increased (Shu et al, 1991;McPherson et al, 1996) risks, we found no substantial relationship with spontaneous abortions, in line with most other investigations (Brinton et al, 1992;Xu et al, 2004;Wernli et al, 2006). Previous studies assessing the effects of induced abortion on endometrial cancer risk have been inconsistent, possibly reflecting small numbers of exposed women.…”

“…Several investigations have suggested that women with extensive breastfeeding histories may be at reduced endometrial cancer risk (Rosenblatt and Thomas, 1995;Salazar-Martinez et al, 1999;Newcomb and Trentham-Dietz, 2000;Wernli et al, 2006), possibly from suppression of ovarian hormones (Petrakis et al, 1987). Although we initially observed reduced risk among subjects who breastfed for 2 or more years, this relation disappeared after adjustment for other risk factors.…”

“…This factor has not generally been regarded as a predictor of endometrial cancer risk (Pettersson et al, 1986;Lesko et al, 1991;Brinton et al, 1992;Parazzini et al, 1998;Xu et al, 2004), despite a number of studies that have demonstrated relatively strong associations (Kvale et al, 1988;Parslov et al, 2000;Hinkula et al, 2002;Wernli et al, 2006). Although it is widely accepted that multiparity may reduce endometrial cancer risk through changes in hormonal profiles, including lowered estradiol and increased sex hormone binding globulin levels (Chubak et al, 2004), underlying mechanisms for reduced risks associated with delayed ages at a first birth are less clear.…”

“…Previous studies assessing the effects of induced abortion on endometrial cancer risk have been inconsistent, possibly reflecting small numbers of exposed women. The majority have shown either no effect (Parazzini et al, 1991;Brinton et al, 1992;Wernli et al, 2006) or possibly some reduction in risk (Shu et al, 1991;Parazzini et al, 1998;Parslov et al, 2000). We had considerable power to evaluate effects of induced abortions, given that they have been legal in Poland for many years.…”

“…Inverse associations with later ages at a first birth have been demonstrated in some studies (Kvale et al, 1988;Albrektsen et al, 1995;Parslov et al, 2000;Wernli et al, 2006), although not in all of them (Lesko et al, 1991;Parazzini et al, 1991Parazzini et al, , 1998Shu et al, 1991;Brinton et al, 1992;McPherson et al, 1996;Lambe et al, 1999). More recently, studies have suggested that risk may decrease with later ages at a last birth (Kvale et al, 1988(Kvale et al, , 1991Lesko et al, 1991;Parazzini et al, 1991Parazzini et al, , 1998Lambe et al, 1999).…”