[A Case of Locally Advanced Breast Cancer Showing Local Enlargement during Chemotherapy, followed by Surgery and Suppression of Recurrence].

A 71-year-old woman was referred to our hospital for a right breast mass urgency. A CT scan revealed a large right breast tumor with skin involvement. Biopsy results confirmed the diagnosis of Luminal-HER2 type invasive ductal carcinoma. Chemotherapy was initiated with a regimen of paclitaxel, trastuzumab, and pertuzumab. Initially, the tumor flattened and significantly decreased in size. However, after 9 months of treatment, disease progression occurred, leading to sequential changes in the treatment regimen to T-DM1 and T-DXd. Despite these efforts, the tumor continued to grow rapidly. At 13 months after starting chemotherapy, the treatment effect was unsatisfactory, prompting a decision to perform a total mastectomy, including resection of the right breast tumor and the pectoralis major muscle, followed by skin grafting. The histopathological effect of the treatment was judged as Grade 1b, with intermediate tumor margins. Postoperatively, the patient received radiation therapy to the chest wall, followed by continued treatment with trastuzumab and pertuzumab. As of 2 years after surgery, no recurrence has been observed.