The 21-year-old chest lumps and pain are mostly considered to be caused by breast diseases, as follows: 1. Breast enlargement, breast fibroids and breast cancer may lead to hard lumps inside the chest and painful sensations. Mammary gland hyperplasia is the most common breast disease, mostly occurring in people with bad moods who have hard lumps in the chest, chest pain, menstrual disorders and poor personality, and the pain will be more intense when the menstruation is approaching due to the influence of the physiological period. If the symptoms are painful and the lump is more active, it is considered to be breast fibroids. 2. Breast cancer may also cause lumps and pain in the breasts, but the incidence of breast cancer in young people is lower. 3.