[A Case of HER2-Positive Breast Cancer with Newly Diagnosed Stage IV That Responded to First-Line Pertuzumab and Trastuzumab-Based Therapy].

A 48-year-old woman who observed swelling and erosion in her left breast was diagnosed with locally advanced, ERnegative, HER2-positive breast cancer with de novo liver metastasis, T4cN1M1, Stage IV . She underwent primary systemic therapy with weekly paclitaxel, and pertuzumab and trastuzumab every 3 weeks. The tumor responded remarkably with 57.0% reduction in 5 weeks of treatment. Because of an anaphylactic shock to paclitaxel in day 8, exchanging to eribulin was considered less toxic than taxane, and was continued for 8 cycles until local relapse. The liver metastasis showed 75.4% reduction. The patient received bilateral mastectomy, which resulted in histological response Grade 1b of the left breast and the right breast of DCIS. After the left thoracic radiation, marginal liver metastasis was observed in the S4 segment on PET-CT. Treatment consisted of docetaxel and dual HER2 blockade therapy in 6 more cycles. As a result, complete remission was achieved.