A 25-year-old woman presents with a concern of having a nontender mass on the breast. PMH : She has no family history of breast cancer. She denies breast leakage or prior medical problems. Examination :  BP: 100/60 mm Hg Except for a 1cm, right, nontender breast mass, her physical examination is unremarkable. Palpation of her right breast reveals a firm, mobile, nontender, rubbery 1-cm mass in the upper outer quadrant. Her neck is supple and the heart and lung examinations are normal.

There are no skin abnormalities noted. No adenopathy is noted. The left breast is normal to palpation. What is the most likely diagnosis? (Answer is posted in the comment section below!) *This case is from the Editorial team of Docplexus and is meant for educative purposes only.