Breast swelling and pain, as well as arm soreness, are considered to be caused by mammary gland hyperplasia and accessory breast syndrome. Mammary gland hyperplasia often manifests as cyclical swelling and pain in the breasts, commonly occurring or worsening before menstruation and alleviating or disappearing after menstruation. While mild cases might not be noticed by patients, severe cases can impact daily life and work. However, some patients do not exhibit obvious cyclical changes, and symptoms can include unilateral or bilateral breast swelling and pain, resembling needle pricks, which can extend to the shoulder, upper limbs, or chest and back areas. A few patients might experience nipple discharge, which can be yellow-green, brown, or bloody. The condition can sometimes persist for a long time, with symptoms automatically disappearing or reducing after menopause. When breast swelling and pain occur, it is necessary to regularly recheck the breast with ultrasound and mammography.