Liu Weiwei (a pseudonym), who is in the 6th grade, was brought by her mother to the Breast Surgery Department of Peking University People’s Hospital one day after the Spring Festival. As soon as she entered the consultation room, Weiwei’s mother hastily lifted up her daughter’s blouse and kept asking Dr. Wang Siyuan, the attending physician, “Doctor, look how well my daughter’s right breast is developing, like a small hill, but the left one has not been moving, what is going on? Do you have a way to make the left breast grow as big as the right? There is a method without surgery?” Dr. Wang first interrupted Weiwei’s mother, then patiently asked Weiwei some questions. As early as six months ago, she noticed that her right breast was getting bigger and harder than her left breast. Especially in the last 3 months, the growth rate of her right breast was significantly faster, but without pain and other discomfort. During the examination, Dr. Wang saw that Weiwei’s left breast was still in an undeveloped state, while the right breast was significantly larger, with thin skin and dilated veins visible on the surface. On palpation, Dr. Wang was surprised to find that Weiwei’s right breast was completely occupied by an apple-sized solid mass with clear borders, smooth surface, hard texture and no pain on touch. Combined with the mammogram results, Dr. Wang diagnosed Weiwei’s right breast as suffering from a giant fibroadenoma of the adolescent breast, with a maximum diameter of nearly 9cm, requiring immediate hospitalization and surgical removal. The left breast, which Weiwei’s mother was worried about, was safe and sound. Vivi’s surgery went well. After nearly one hour of effort, Dr. Wang removed a 9.0 cm x 6.5 cm fibroadenoma from Vivi’s right breast. During surgery, the fibroadenoma was seen to have an intact envelope and was locally lobulated. The surrounding normal breast glandular tissue was severely compressed and displaced. The postoperative paraffin pathology confirmed the diagnosis of juvenile fibroadenoma, which is a benign lesion of the breast. When she was discharged from the hospital, Dr. Wang Siyuan especially reminded Wei Wei and her daughter that girls should take care of their breast health and start breast self-examination since they enter puberty, because breast tumors can take root and sprout during this period. It is a rare kind of fibroadenoma, which is benign and its cause is unknown. Its occurrence may be closely related to the estrogen level in the body. As the age of breast cancer is getting younger and younger, it is no longer a rare case that a girl develops breast cancer in her teens. If a girl finds a lump in her breast, especially if it grows rapidly within a short period of time, she should consult a breast specialist in time.