Stage IIIB triple-negative metaplastic breast cancer: urgent mastectomy and reconstruction after rapid progression on neoadjuvant therapy

What happened, in summary

This 47-year-old woman had a right breast fibroadenoma that had been known for 10 years but began enlarging over 6 months. Core needle biopsy showed invasive carcinoma, and final pathology identified triple-negative metaplastic breast carcinoma, nuclear grade 3. The tumor was initially classified as cT2N0M0, Stage IIA. She had no diabetes and had never smoked. Treatment began with the KEYNOTE-522 regimen: pembrolizumab every 3 weeks, paclitaxel weekly, and carboplatin every 3 weeks for the first 12 weeks. The cancer progressed extremely quickly. One week after treatment began, the tumor grew from 40 mm to 68 mm; 1 week later it reached 80 mm, with axillary lymph node swelling and skin redness. She was restaged as cT4bN1M0, Stage IIIB, and urgent surgery was needed to prevent tumor rupture. Surgeons performed right mastectomy with a 1 cm margin around suspected skin invasion. Because only thin pectoralis muscle and fascia remained between tumor and chest wall, those structures were also removed, and axillary lymph nodes were dissected to level 2. Reconstruction used an internal mammary artery perforator flap to cover exposed ribs and sternum, plus a meshed thigh skin graft over the pectoralis major muscle. Partial flap necrosis occurred but healed within 3 weeks. Final pathology confirmed triple-negative metaplastic carcinoma; all lymph nodes were negative, and treatment effect was grade 2a. Chemotherapy resumed 4 weeks after surgery, radiation began 4.5 months later, and levothyroxine was started for hypothyroidism. At 18 months, she was disease-free and remained under surveillance. She later had a dog-ear deformity corrected under local anesthesia, but she continued to have distress about the mesh skin-graft appearance and received psychological support for that survivorship concern.