A lump on top of the breast with a warm feeling may be caused by lobular hyperplasia, cystic hyperplasia of the breast, acute mastitis and other reasons. 1. Lobular hyperplasia: endocrine disorders lead to lobular hyperplasia, which is clinically manifested as small nodules in the mammary gland, and before menstruation, the mammary gland will experience cyclic pain accompanied by symptoms of fever. 2. Cystic hyperplasia of the breast: due to the disorder of female hormone metabolism and the imbalance of the ratio of estrogen to progesterone, it will lead to the phenomenon of breast lumps and fever. The size and pain of the lumps are also related to emotional changes, and most women’s symptoms worsen before menstruation and after exertion. 3. Acute mastitis: Acute mastitis is an acute suppurative infection of the breast, an inflammation of the connective tissue in and around the ducts of the breast, which may result in redness, swelling, heat, pain, and a localized lump in the breast. When there is a lump on top of the breast and a feeling of warmth you should go to the hospital in time and be treated under the doctor’s advice.