Erythematous, friable nipple with loss of protrusion · history of breastfeeding · Dx?

A 34-year-old healthy woman presented to the breast surgical oncology clinic with skin changes to her left nipple after being referred by her primary care provider. She attributed the skin changes to shearing from breastfeeding her third child 5 years earlier. Physical examination revealed an erythematous and friable nipple with loss of protrusion. The patient reported routine bleeding from her nipple, but said the skin changes had remained stable and denied any breast masses. The patient's last mammogram was 2.5 years earlier and had only been remarkable for bilateral benign calcifications.