A 52-year-old woman presented with redness and swelling with a peau d'orange appearance in the whole right breast. Ultrasound revealed elevated subcutaneus fat density and a diffuse hypoechoic area. She was diagnosed with inflammatory breast cancer(T4dN2M0, Stage III B of the HER2 subtype). After 4 courses of EC treatment as primary systemic therapy, the hypoechoic area was still present. Subsequent chemotherapy with pertuzumab, trastuzumab, and docetaxel was effective, as hypoechoic area was not observed on ultrasound. She underwent mastectomy and axillary dissection, and pathological examination revealed pCR. At present, 2 years after surgery, the patient is alive with no reccurence.