J Cancer 2018; 9(23):4422-4429. doi:10.7150/jca.26242

Research Paper

Age at First Birth and the Risk of Endometrial Cancer Incidence: A Pooled Analysis of Two Prospective Cohort Studies among Japanese Women

Yumi Sugawara1✉, Kemmyo Sugiyama1, Yasutake Tomata1, Seiki Kanemura2, Akira Fukao3, Ichiro Tsuji1

1. Division of Epidemiology, Department of Health Informatics and Public Health, Tohoku University School of Public Health, Graduate School of Medicine, Sendai, Japan
2. Division of Cancer Epidemiology and Prevention, Miyagi Cancer Center Research Institute, Natori, Japan
3. Department of Public Health, Yamagata University Graduate School of Medicine, Yamagata, Japan

Abstract

Background: Age at first birth has been increasing among women in developed countries. Meanwhile, endometrial cancer has also been increasing worldwide, being one of the most common female hormone-related cancers. The purpose of this study was to examine the association between age at first birth and the risk of endometrial cancer among Japanese women, and to examine the hypothesis that the recent increase in endometrial cancer incidence can be partly explained by the trend for increasing age at first birth.

Methods: We conducted a pooled analysis of two prospective studies among residents in Miyagi Prefecture in rural northern in Japan. The Miyagi Cohort Study started in 1990 and included 21,455 parous women. The Ohsaki Cohort Study started in 1994 and included 17,287 parous women. The subjects responded to a self-administrated questionnaire including reproductive factors such as age at first birth. Incident cases of cancer were identified through linkage to the Miyagi Prefectural Cancer Registry, which covers the study area.

Results: In a consortium of two prospective studies with 598,933 person-years, we identified 105 incident case of endometrial cancer. Compared with women aged 22 years or less at first birth, multivariate hazard ratios (HRs) and 95% confidence intervals (CIs) for the risk of endometrial cancer were 0.79 (0.49-1.26) for women aged 23 to 25 years at first birth, and 0.53 (0.28-1.00) for those aged 26 years and older (p-trend<0.05).

Conclusion: This pooled analysis of two prospective studies does not support the hypothesis that the recent increase in the incidence of endometrial cancer can be partly explained by the increase in the age at first birth.

Keywords: age at first birth, endometrial cancer, incidence, Japanese women, prospective cohort study

This is an open access article distributed under the terms of the Creative Commons Attribution (CC BY-NC) license (https://creativecommons.org/licenses/by-nc/4.0/). See http://ivyspring.com/terms for full terms and conditions.
How to cite this article:
Sugawara Y, Sugiyama K, Tomata Y, Kanemura S, Fukao A, Tsuji I. Age at First Birth and the Risk of Endometrial Cancer Incidence: A Pooled Analysis of Two Prospective Cohort Studies among Japanese Women. J Cancer 2018; 9(23):4422-4429. doi:10.7150/jca.26242. Available from http://www.jcancer.org/v09p4422.htm