Smoking, earlier menarche and low parity as independent risk factors for gynecologic cancers in Japanese: a case-control study.

During recent decades, the incidence of gynecologic cancers, i.e., cancers of the cervix, endometrium and ovary, has increased in Japan. However, risk factors of gynecologic cancers have not been fully clarified in Japan. To investigate common and site-specific risk factors among gynecologic cancers, we conducted a hospital-based case-control study. The cases, i.e., 151 cervical, 103 endometrial and 141 ovarian cancer cases and the controls (n = 2016) were selected from female patients aged 30 and over, who were admitted to a single hospital in Miyagi Prefecture from 1997 to 2003. Information on reproductive factors, exogenous hormone use, and lifestyles including smoking was collected using a self-administered questionnaire. Smoking was significantly associated with an increased risk of cervical cancer. A dose-response relationship with the number of cigarettes per day was also observed (p for trend = 0.004). Older age at menarche was associated with a decreased risk of endometrial and ovarian cancers. For these cancers, the decreased risk was detected with increasing parity number (endometrium, p for trend = 0.0001; ovary, p = 0.0002). There was no significant association between exogenous hormone use and gynecologic cancer risk. The results indicate that smoking is a major risk factor of cervical cancer. In addition, hormonal factors, which are related to early onset of menarche and low parity, are common risk factors for endometrial and ovarian cancers. The increase in female smokers and the decrease in fertility rate may contribute to the increase in gynecologic cancer incidence in Japan.