18-year-old girls have hard lumps in the chest is no more than breast hyperplasia, breast fibroma or even breast cancer, while 18-year-old boys are very likely to be malignant lesions. Specific reasons are analyzed as follows: 1, endocrine reasons. Hormone level fluctuations in the body will be breast lobular hyperplasia, adolescent girls are very easy to occur, often accompanied by premenstrual syndrome, such as breast pain during menstruation, redness, warmth, this benign disease of the lump smooth, can slide, not adhesion, commonly found in the mammary gland hyperplasia, mammary fibrocystic degeneration. 2, lymph node lesions. Due to inflammation stimulation will lead to the enlargement of lymph nodes, the place can obviously touch the hard lump, inflammation is obvious when there will be pain, most of them do not feel anything. A short time without enlargement can be ignored, if suddenly enlarged, tingling, to prevent the possibility of deterioration.3, breast cancer, cancer symptoms are very typical.