MSFinals-6318

MSFinals-6318

A 35 year old woman presents with a 4 week history of increasing redness over her right breast. She is not breastfeeding and reports feeling generally well. Although the area is not painful, she is worried as it has not improved. Upon examination, there is significant swelling and erythema, but no discharge, nipple changes, or palpable masses. Vital signs are normal and she has no fever. Blood test results are as follows:
– White blood cell count: 6×10^9/L
– C-reactive protein: 4 mg/L
– CA 15-3 level: 57 Units/ml (normal range <30 Units/ml)
What is the most likely diagnosis?