The causes of breast enlargement in men are considered to be related to natural changes in hormones, and oncologic diseases cannot be ruled out. In general, the exact pathogenesis of breast enlargement in men is not clear, but it may be related to an imbalance in estrogen levels. In the case of estrogen stimulation, it can cause breast tissue to proliferate. For example, a newborn male baby will have high maternal estrogen levels, which will cause breast development due to the predominance of estrogen’s promotional effect on the mammary glands. It should be noted that when men have testicular spermatogonia, teratoma, lung cancer, and tumors of the pituitary gland, adrenal glands, hypothalamus and other endocrine organs, it will also further contribute to the development of mammary hyperplasia in men, which is mainly related to the imbalance of hormone secretion in the body. In addition, some patients may also suffer from breast enlargement due to exogenous intake of estrogen for various reasons. It is recommended that male patients with symptoms of breast hyperplasia should take into account their own conditions and cooperate with their doctors to choose the appropriate examination and treatment, so as not to delay the condition.