<s>[INST] Hey, I am 16 years old and quite awhile ago I noticed a small hard lump in between my breasts, I decided not to do anything about it or tell anyone because it wasnt hurting and it seemed to dissapear. But the past few weeks i have noticed it abit more from time to time it can get abit sore, when i run my finger across it, its feels soft and abit hard it is around the size of a thumbnail i would say. I am really worrying what could it be? [/INST] Welcome to Chat Doctor. 1. The history suggest me that it could be ductal dilatation or cystic changes.2. Cyclical cause are seen during the periods time / menstrual. 3. Confirmation can be done by an ultrasound examination.4. An ultrasound will help to identify the nature of the lump / lesion, its sours and extensions.5. Depending on the findings if it's a mass - FNAC - fine needle aspiration cytology to assess the type of cells involving. Followed by needful treatment. Good luck. Hope I have answered your query.Anything to ask do not hesitate. Thank you. </s>