Tohoku J. Exp. Med., 2006, 208(2)

Lactation and Risk of Endometrial Cancer in Japan: A Case-Control Study

CHIKAKO OKAMURA, YOSHITAKA TSUBONO,¹ KIYOSHI ITO, HITOSHI NIIKURA, TADAO TAKANO, SATORU NAGASE, KOHSUKE YOSHINAGA, YUKIHIRO TERADA, TAKASHI MURAKAMI, SHINJI SATO,² DAISUKE AOKI,³ TOSHIKO JOBO,⁴ KUNIHIRO OKAMURA and NOBUO YAEGASHI

Department of Obstetrics and Gynecology, Tohoku University Graduate School of Medicine, Sendai, Japan, ¹Tohoku University School of Public Policy, Sendai, Japan, ²SS Ladies Clinic, Sendai, Japan, ³Department of Obstetrics and Gynecology, Keio University School of Medicine, Tokyo, Japan, and ⁴Department of Obstetrics and Gynecology, Kitasato University School of Medicine, Kanagawa, Japan

The incidence of endometrial cancer is rapidly increasing in Japan. Although the risk factors in European populations have been well described, there are few epidemiologic studies regarding risk factors for endometrial cancer in Japanese women. This hospital-based case-control study among Japanese women was carried out from 1998 to 2000. The cases were selected from women with endometrial cancer (n =155), and the controls selected from women attending the university gynecological outpatient clinic for cervical cancer screening (n = 96). Subjects were interviewed to ascertain breast feeding practices, contraceptive usage, as well as potential risk factors for endometrial cancer. We observed a lower risk of endometrial cancer associated with oral contraceptive (OC) and a higher risk associated with higher body mass index (BMI), and older ages at first and last delivery. Gravidity reduced odds ratio (OR) for endometerial cancer to 0.34 (95% confidence interval [CI] 0.13-0.92). Compared with parous women who had never breastfed, the multivariate OR for women with a history of breastfeeding was 0.37 (95% CI, 0.17-0.82). Additionally, a greater lapse of time since breastfeeding increased OR for endometrial cancer by over three times. In conclusion, the present study has indicated that breastfeeding reduces the risk of endometrial cancer in Japanese women.

keywords —— endometrial cancer; breastfeeding; risk factor; case-control study

© 2006 Tohoku University Medical Press

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Tohoku J. Exp. Med., 2006, 208, 109-115

Correspondence: Nobuo Yaegashi, Department of Obstetrics and Gynecology, Tohoku University Graduate School of Medicine, 1-1 Seiryomachi, Aoba-ku, Sendai 980-8574, Japan.

e-mail: yaegashi@mail.tains.tohoku.ac.jp