Prevalence of Breast Cancer Risk Factors in Japan

Breast cancer is the most common type of cancer in women worldwide. Although the incidence of breast cancer is still on an increasing trend, there are few studies concerning breast cancer risk factors in Japan. Therefore, we conducted an Internet survey investigating the prevalence of risk factors for breast cancer. We conducted an Internet survey using opt-in panels in women aged from 20 to 70 years. The survey items consisted of potential and proven risk factors for breast cancer such as age at menarche, menopausal status, premenopausal use of oral contraceptives, postmenopausal use of hormones, parity, height, alcohol consumption and family history of breast cancer. Subjects comprised 2002 persons who were matched for sex, age and residential area with the National Census in 2005. Statistically significant trends were observed for most factors: age at menarche is becoming lower, age at first birth is higher, height is higher, the proportion of women who have given birth is smaller and the proportion of women who drink alcohol is larger. We showed a clear increase in the prevalence of risk factors for breast cancer. Based on the results, the incidence of breast cancer in Japan may be increasing for at least a few decades.