The accessory mammary gland is the most common breast deformity, especially in the axilla, anterior chest and vulva, and less commonly in the cheeks, ears, neck, upper extremities, ribs, shoulders, hips, buttocks and femur, etc. Parammary glands account for about 2-6% of adult women. Parammary glands with nipple and glandular tissue are easy to diagnose clinically, while those with subcutaneous lumps must be diagnosed by histological examination. The incidence of adenocarcinoma of the parametrium is less common. Foreign literature reports that the incidence of adenocarcinoma of the parametrium accounts for 0.2-0.6% of all breast cancers, while domestic literature reports that it accounts for 0.1-0.15% of all breast cancers. Diagnosis: The main clinical manifestation of parametrial adenocarcinoma is an axillary mass with hard and indistinct borders, which may be fixed to the skin or adhered to the base, and the surface skin may become edematous. Pre-operative ultrasound and mammography can be helpful for diagnosis. Ultrasound examination of the axilla of parametrial adenocarcinoma shows a hypoechoic axillary lesion with poorly defined and irregular internal echogenicity, while mammography shows a shadow of a mass with irregular margins in the axilla, and the local skin may be thickened. Preoperative needle aspiration puncture biopsy can help clarify the diagnosis and guide the development of a treatment plan. Prognosis: The overall survival rate is 35.3% at 5 years (lower than the overall survival rate of 66.8% at 5 years after breast cancer surgery) and 77.8% at 3 years; the tumor-free survival rate is 28.6% at 5 years and 63.6% at 3 years. The literature reports that paraneoplastic breast cancer can develop gastrointestinal and chest wall metastases, but most often metastasize to bone, liver and lung. There are several reasons for the low 5-year survival rate: firstly, the metastasis of parametrial breast cancer occurs earlier and the prognosis is worse because of the adjacent lymph node rich area; secondly, the abnormal location of parametrial breast is easy to be missed and misdiagnosed; meanwhile, because the tumor has no obvious local pain or lacks other concomitant symptoms, patients do not pay enough attention to it and usually come to the clinic at a later stage. Some patients come to the clinic only when the tumor is 10 cm in diameter or six years old. 52.6% of the patients have stage IV disease and 76.3% of the patients have lymph node metastasis confirmed by postoperative pathology. Treatment: The treatment of parametrial breast cancer should follow the principle of comprehensive treatment based on surgery in order to improve the survival of patients. Therefore, prophylactic resection is not recommended for asymptomatic parammary glands without masses; however, some literature reports that the malignancy rate of patients with parammary gland tumors is 24%-63%, so prophylactic resection is feasible for symptomatic parammary glands to prevent malignancy.