Fibroadenoma of the breast is a common tumor among adolescent women, with the most common age of onset being 20 to 30 years old. Most of them are clinically solitary, but 15-20% of cases can be multiple. The occurrence of fibroadenoma is related to the increase of estrogen level in the body, and the tumor rarely occurs before menarche or after menopause. Etiology The gross specimen of fibroadenoma can be seen as follows: fibroadenoma is clearly demarcated from the surrounding breast tissue, movable, tough and smooth surface. The tumor is mostly round or oval in shape and often has an intact thin fiber envelope on its surface. When there are more fibrous components, the tumor surface is grayish white, translucent, tough and elastic; when there are abundant epithelial components, the surface is light pink, fine granular, or even papillary, turning outward, with soft texture. Under light microscopy, fibroadenoma of the breast can be divided into three pathological types: intraductal, periductal and mixed, according to the degree of growth of the fibrous and epithelial components and their mutual structural relationship. 1. Intraductal type: The proliferating fibrous tissue in the mesenchyme compresses the ducts, causing them to elongate, bend and deform, and in severe cases, it seems that the mesenchymal components invade the duct lumen. The epithelium of the glandular duct is squeezed and atrophied into flat shape. The fibrous tissues inside the tumor are looser and can be mucus-like. 2. Peritubular type: epithelial components are mixed with fibrous components, and the glandular ducts are round, oval or irregular in shape, not extruded by proliferating fibrous tissues. The lumen is composed of two layers of epithelial cells, the inner layer is a single layer of cuboidal or columnar epithelium, and the outer layer is a myoepithelium with translucent cytoplasm. The epithelial component may be mildly hyperplastic. The fibrous tissue within the tumor is hyperplastic and surrounds the glandular ducts, which can be loose or dense, and even have collagen degeneration. 3.Mixed type: pathological changes of intraductal and periductal types exist simultaneously. Clinical manifestations The most important clinical manifestation of breast fibroadenoma is breast lumps, and in most cases, breast lumps are the only symptom of this disease. The lumps are usually found unintentionally by the patient and are usually not painful and do not change with the menstrual cycle. In a small number of cases, premenstrual breast tenderness may be present when fibroadenoma and mastocytosis coexist. The lumps of fibroadenoma are usually found in the outer upper quadrant of the breast. Adenomas are often solitary, but may be multiple. Adenomas are round or ovoid in shape, with a diameter of 1 to 3 cm being more common, or smaller or larger, and occasionally huge. The surface is smooth, the texture is tough, the boundary is clear, there is no adhesion with the skin and surrounding tissues, the mobility is large, and there is a sliding sensation when touched. The axillary lymph nodes are not enlarged. Most adenomas are not painful and do not have tenderness. The size and nature of the mass does not usually vary with the menstrual cycle. The lump usually grows slowly and may remain unchanged for several years, but may increase rapidly during pregnancy and lactation, and in some cases may become sarcomatous at this time. Diagnosis and Differentiation Because the breast is a superficial organ, it is relatively easy to diagnose fibroadenomas that occur in the breast. The diagnosis of mammary fibroadenoma is based on the following: 1. The disease usually occurs in adolescent women, and is most common between the ages of 18 and 25. 2. The tumor mostly occurs in one breast, often solitary, and the outer upper quadrant of the breast is the most common. The lump is usually round or oval, with different sizes, hard texture, smooth surface, clear boundary, large mobility, no adhesion with surrounding tissues, no pain and tenderness. It grows slowly and does not septicize and ulcerate. It is not related to menstrual cycle. 3.Molybdenum X-ray and other imaging examinations can help the diagnosis. If necessary, needle aspiration cytology or biopsy of the mass may be performed for a definitive diagnosis. It should be noted that if a breast lump appears in a woman over 35 years old, especially after menopause, the diagnosis should not be made lightly even if the lump resembles a breast fibroadenoma, and the diagnosis of fibroadenoma should be made only after the possibility of breast cancer has been ruled out, and surgery should be preferred. What are the differential diagnoses for fibroadenoma of the breast? Breast lumps in mammary fibroadenoma should be differentiated from other diseases that also have breast lumps as the main clinical manifestation, such as mastocytosis, breast cysts and breast cancer. 1. Adenofibroadenoma and mastoproliferative disease: Both can be seen as breast lumps, single or multiple, with a firm texture. However, the lumps of breast fibroadenoma are more common in unilateral solitary cases, mostly round or ovoid, with clear borders and high mobility, and are painless and painful to touch, with no obvious relationship with menstrual cycle. The lumps are often painful to the touch and can change with the menstrual cycle, and the whole breast is often distended before menstruation and can be relieved after menstruation. If necessary, relevant auxiliary examinations can be carried out to differentiate them, such as mammography, and a circular or ovoid shadow with uniform density can be seen around the fibroadenoma, which can be differentiated from mastocytosis. 2, adenofibroadenoma and breast cyst: both can be seen as painless breast lumps, mostly unilateral and solitary, with clear borders and smooth surfaces. However, the lump of breast fibroadenoma is slightly harder and tougher than cyst, without cystic sensation, with greater mobility than cyst, and the most common age of onset is 18-25 years old; the lump of breast cumulus cyst has cystic sensation, with less mobility than adenoma, and mostly occurs during pregnancy and lactation, while simple breast cyst has clinical features of mastoproliferative disease in addition to cyst. In addition, the lump can be differentiated by puncture. Adenoma is a solid lump with no fluid, while cysts can be extracted with milk-like or plasma fluid. 3. Breast fibroadenoma and breast cancer: both of them can be seen as painless breast lumps, mostly solitary. Breast lumps of fibroadenoma are round or ovoid, with firm texture, smooth surface, clear border, and high mobility, and grow slowly. The surface of the lump is not smooth and the mobility is poor, and it is easy to adhere to the skin and surrounding tissues. On mammography, fibroadenoma can be seen as a round or ovoid shadow with a circular transparent halo around it, while breast cancer can be seen as a lump shadow, small calcified spots, abnormal vascular shadow and burr. If necessary, needle aspiration cytology and biopsy can provide histological evidence for differentiation. Treatment The most effective treatment for fibroadenoma of the breast is surgery. In addition, there are also Chinese herbal treatments and hormone therapy for the cause of the disease. Currently, in addition to surgery, Chinese herbal medicine is mainly used, and hormone therapy is not commonly used. Although surgery is the most effective treatment for breast fibroadenoma, it does not mean that surgery is needed as soon as the adenoma is found, but the timing and indications for surgery should be strictly controlled and cannot be generalized. For example, if an adenoma is not large in an unmarried woman around 20 years old, immediate surgery is not advisable, clinical observation should be the main focus, and Chinese herbal medicine treatment can be given if necessary; if a young woman is married and her adenoma is over 1cm, surgery is advisable before pregnancy; if a new adenoma appears during pregnancy and lactation, the growth of the lump should be observed first, and if the lump grows rapidly, immediate surgery should be performed; if an adenoma is found in a woman over 35 years old, especially if the lump grows rapidly, surgery should be performed immediately. If adenomas are found in women over 35 years of age, especially in postmenopausal women, they should be removed immediately and examined by intraoperative frozen section; for cases of recurrence in the same place after surgery, we should be alert to the possibility of malignant change. The possibility of malignant change can be reduced by taking herbal medicine after surgery. Surgery for mammary fibroadenoma requires attention to the function and aesthetics of the breast while treating the disease. Since most of the patients are young women and some of them are not married yet, when the fibroadenoma needs to be removed surgically, a radial incision centered on the nipple should be made in consideration of the patient’s future breastfeeding needs, so as not to damage the milk ducts; the incision should be as small and beautiful as possible, so that the scar after healing is reduced to a minimum. In addition, pathological examination should be done routinely when performing surgery for fibroadenoma. It is very wrong to think that adenoma is benign and rarely malignant anyway, so there is no harm in not doing pathological examination. It is important to know that routine pathological examination and preservation of tissue blocks for a period of time is not only beneficial for the improvement of clinical diagnostic ability, but also for research and improvement of academic level of the hospital.