Hard lumps in the left breast of 6-7 years old girls may be related to precocious puberty, lymphadenitis, etc. The causes are different, and further examination is needed to clarify the cause of the disease and carry out targeted treatment. 1. Central precocious puberty: it may be due to the excess of sex hormones caused by various factors, leading to central precocious puberty in girls, which may result in the phenomenon of breast enlargement and hard lumps, and it can be treated by medication, such as treprostinil, leuprolide, etc., to inhibit the process of sexual development. If the precocious puberty is secondary, it can be treated by surgery if necessary to remove the cause of the disease. 2. Lymphadenitis: non-specific inflammation of the lymph nodes in the chest due to a variety of reasons, under the stimulation of inflammation, the lymph nodes appear to be swollen, thus causing the phenomenon of hard lumps in the left breast, which can be treated by penicillin, azithromycin and other drugs. 6-7 year old girl left breast hard lump may also have other reasons, such as mastitis, etc., it is recommended to go to the hospital in time, improve the examination to clarify the cause of the disease, give targeted treatment or treatment.