Non-metastatic metaplastic triple-negative breast cancer with residual disease after chemotherapy

What happened, in summary

This 41-year-old woman first noticed a right breast lump in February 2024. It was initially treated as a possible breast abscess, and she underwent incision and drainage with tissue biopsy. Pathology showed malignancy, leading to further breast imaging and biopsy. The right breast mass was large, about 12 x 8 cm on examination, and core biopsy showed invasive carcinoma with squamous features. The tumor was p63-positive, CK5/6-positive, GATA3-positive, PR-negative, HER2 0, and clinically consistent with a triple-negative phenotype despite faint ER staining in about 10% of cells. Ki-67 was high at 90%. Axillary node biopsy showed no metastasis, and the clinical diagnosis was right mammary metaplastic squamous cell carcinoma, cT3N0M0. This meant the cancer was large and locally high-risk, but the available staging did not show distant spread.

She began neoadjuvant TEC chemotherapy with nab-paclitaxel, epirubicin, and cyclophosphamide. During the fourth cycle, a wound infection with multidrug-resistant Staphylococcus aureus was treated successfully with levofloxacin. Her tumor initially shrank after the first 5 cycles, but after the sixth cycle imaging showed disease progression, suggesting acquired resistance to the regimen.

On 29 August 2024, she underwent modified radical mastectomy. Final pathology showed residual tumor measuring 7.0 x 4.8 x 3.0 cm with skin invasion and ulceration. Treatment response was minimal by Miller-Payne grade 1, but all 21 lymph nodes were negative. Because of the large original tumor and high-risk residual disease, postoperative care included adjuvant radiotherapy to the chest wall and regional nodes, along with metronomic capecitabine to reduce recurrence risk.