A case of reconstruction for triple-negative metaplastic breast cancer that enlarged rapidly during neoadjuvant immunochemotherapy.

We report a case of reconstruction for triple-negative metaplastic breast cancer that rapidly enlarged during neoadjuvant immunochemotherapy, requiring semi-emergency surgery. A 47-year-old female with metaplastic carcinoma (cT2N0M0, stage IIA) received pembrolizumab, paclitaxel, and carboplatin in a neoadjuvant fashion. Rapid tumor enlargement and axillary lymph node swelling occurred during the first cycle of immunochemotherapy, necessitating semi-emergency surgery to prevent tumor rupture (cT4bN1M0, stage IIIB). Right mastectomy with partial pectoralis major muscle resection and axillary lymph node dissection were performed, exposing the ribs and sternum. Reconstruction utilized an internal mammary artery perforator flap with caudal rotation-advancement, followed by meshed skin grafting. Despite partial epidermal necrosis, wound closure was achieved after 3 weeks. Chemotherapy resumed 4 weeks after surgery; radiation therapy was initiated 4.5 months later. The patient remains disease-free 18 months after surgery. To our knowledge, mastectomy with pectoralis major resection and internal mammary artery perforator flap reconstruction for a triple-negative metaplastic breast cancer that had rapidly progressed during neoadjuvant therapy has not been previously reported.