<s>[INST] My 18 month old has has a unilateral lump in her left breast. I m not entirely happy with the results I got, I was told it s either a fat deposit or a fibroadenoma. I ve been doing a bit of reading and as they have suggested biopsy in 6-8 weeks if it has increased in size, I am worried if these could be mistaken for thelarche? Or if there is something in the iages that rule that out? I have no doubt a biopsy would be traumatic for my 18 month old, the ultrasound itself was bad enough. And I am also worried if it is just a benign lump that the biopsy could cause some sort of damage? She is also still breastfeed, she eats food, but also has breastmilk throughout the day. The lump has been there for a month that I know of. It definitely has not shrunk, but I am also unsure if it has increased in size. [/INST] Hi...if I were your pediatrician or pediatric surgeon I would definitely have advised you the same thing - to go ahead with biopsy. Biopsy would be done under anesthesia unlike an ultrasound which is done when the kid is awake. So it would not be traumatic to the kid. Thelarche should be bilateral that is both sides - but as this is unilateral I definitly suggest doing a biopsy and arriving at a diagnosis as soon as possible.regards - Dr. Sumanth </s>