Fibroadenomas are benign (non-cancerous) and most are asymptomatic and painless. They appear as well-circumscribed, rubbery, mobile masses. Most are solitary, but up to 25 percent of patients have multiple tumors.
Adult women with fibroadenomas have a higher risk for developing breast cancer than women of similar age in the general population. Features of the fibroadenoma seen under the microscope influence this risk. There have been no documented reports of malignancy occurring within a preexisting fibroadenoma in an adolescent. Small fibroadenomas typically do not distort the breast, and over half of these lesions will decrease in size over 5 years. For these reasons, most fibroadenomas can be followed with yearly examinations as appears to be your case. If you removed every single fibroadenoma in every patient more than half of those operations would be unnecessary. However, because this conservative approach can be a source of anxiety for the patient and her family, excision rather than observation is frequently the treatment of choice.
Fibroadenomas can be removed by enucleation without removal of any surrounding breast tissue with minimal risk of local recurrence. Mastectomy is not required, and no other treatment is required. In your specific case the questions should be what happens if you get the augmentation and leave the fibroadenoma in place. The answer is most likely nothing but since the surgeon is in there anyways examination of the fibroadenoma or part of it under the microscope would not be a bad idea. If it is easier to remove at the time of breast augmentation vs. afterward should it become problematic that should also be taken into account.
My response to your question/post does not represent formal medical advice or constitute a doctor patient relationship. You need to consult with i.e. personally see a board certified plastic surgeon in order to receive a formal evaluation and develop a doctor patient relationship.