ABSTRACT
There is strong evidence that reproductive factors and endogenous sex hormones are important in the etiology of breast cancer. As for many other malignancies the incidence of breast cancer shows a continuous increase with age, until around 50 years. Thereafter when the average woman enters a postmenopausal state there is a decline in the incidence1. The number of ovulatory menstrual cycles during the reproductive period of a woman’s life has a positive correlation with breast cancer risk2. Women with an early menarche and late menopause have an increase in relative risk of around 1.5-2, whereas an early menopause has a protective effect3. Early childbirth, multiple pregnancies and lactation have been associated with a reduced risk of breast cancer, while the increased incidence following childbirth after the age of 30 implies an age-dependent increase in risk4. The risk of breast cancer seems to rise in parallel with an increase of endogenous estradiol levels5. Young women with obesity have a lower breast cancer risk, whereas obesity after the menopause has been connected with an increase in breast cancer. This could relate to hormonal factors, since obese young women often have anovulatory cycles, and obese elderly woman with more fatty tissue may have an enhanced local production of estrogens by peripheral aromatization of androgen precursors6. In fact, endogenous estrogen levels may be the key factor for a variety of associations reported, such as body mass, bone mass, reproductive history, menarche, menopause, and dietary habits. This concept is also supported by the fact that an early menopause or oophorectomy is strongly protective and also increases survival in young breast-cancer patients1,7.
