Risk factors for the development of breast cancer include all of the following, EXCEPT:

The anti-estrogenic action produced by progesterone may be responsible for a reduction of the incidence of breast cancer in multiparous women. Hyperestrinism is the key factor that enhances predisposition of the development of breast cancer. Use of oral contraceptives or estrogen replacement therapy for postmenopausal symptoms for a period of 5-10 years does not significantly increase the chances of development of breast cancer. However, prolonged use of estrogen in excess of ten years may increase the chance of development of breast cancer. Chances are higher in women with other known risk factors such as a family history of breast cancer.