A 20 year old woman notes a form, 1 to 2 cm mass in her left breast. There is no nipple discharge and no pain.No axillary adenopathy is present. The overlying skin of the breast appears normal. Mammography confirms the presence of rounded density, which has no microcalcifications and reveals no lesions of the opposite breast, Which of the following is the most likely diagnosis?
Select one of the following: