Fibroadenoma suffered by eighteen-year-old girl is a common tumor among adolescent females, and elevated absolute value of endogenous or exogenous estrogen level is the main cause of its development. 1. Elevated endogenous estrogen: the occurrence of breast fibroadenoma is mainly related to the hormonal imbalance in the body. In the period of ovarian function, the fibroblasts in the lobules are abnormally sensitive to estrogen, leading to the occurrence of breast fibroadenoma. 2. Elevation of exogenous estrogen: besides, some researches show that with the increase of modernized and industrialized products, chemical substances containing phenol A ring can be degraded into a kind of long half-life steroid hormone simulating estradiol after entering into the human body, which is called exogenous estrogen or environmental estrogen, and this kind of estrogen can stimulate the growth of fibroadenomas as well. At the same time, the occurrence of breast fibrofibroma may also have some genetic factors. It is recommended that patients suffering from fibroadenoma should consult with regular hospitals for regular review and standardized treatment under the guidance of doctors.