Risk factors among young women with endometrial cancer: a Danish case-control study.

OBJECTIVE This study was undertaken to identify and quantify risk factors for endometrial cancer among young women. STUDY DESIGN This case-control study included all Danish women <50 years old who had endometrial cancer diagnosed during the period 1987 to 1994. A total of 237 case patients and 538 population control subjects matched with the case patients for age and residence were included in the analysis. RESULTS Women with a family history of endometrial cancer had an odds ratio for endometrial cancer of 2.1 (95% confidence interval, 1.1-3.8)). Completion of 1 term pregnancy implied an odds ratio of 0.6 (95% confidence interval, 0.3-1.1). The risk of endometrial cancer decreased significantly with increasing age at first birth and with the number of induced abortions. Use of oral contraceptives for 1 to 5 years decreased the risk of endometrial cancer (odds ratio, 0.2; 95% confidence interval, 0.1-0.3). The odds ratio for endometrial cancer among women who received hormone replacement therapy for 1 to 5 years was 3.1 (95% confidence interval, 1.4-7.0). Body mass index was not demonstrated to be an independent risk factor in this study. The protective impacts of the different exposures (risk factors) can be expressed as etiologic fractions, which indicate how much each exposure reduces the occurrence of endometrial cancer compared with a situation without the existence of that particular exposure. These fractions were as follows: oral contraceptive use for > or =1 year, -45%; 2 term pregnancies, -88%; age > or =30 y when giving birth for the first time, -38%; and a history of incomplete pregnancy, -16%. CONCLUSION A number of risk factors for endometrial cancer are common to premenopausal and postmenopausal women: family history, reproductive history, hormone replacement therapy, and the use of oral contraceptives. Among young women reproductive variables imply the greatest prophylactic potential.