Metaplastic triple-negative breast cancer: near-complete response to taxane/carboplatin before surgery

What happened, in summary

This 39-year-old woman was reevaluated after a right breast tumor had been incompletely excised with positive margins and after nodules were also seen in the left breast. Her symptoms began in July 2022 with a right breast mass. Initial biopsy did not confirm malignancy, but the mass enlarged on follow-up mammography. On 18 October 2022, she underwent partial mastectomy of the right breast. Pathology showed metaplastic carcinoma with mesenchymal differentiation, Nottingham grade 3, measuring 35 mm, with positive surgical margins. ER, PR, and HER2 were all negative, making the cancer triple-negative. A PET scan soon afterward showed postoperative right breast disease extending near the right pectoralis major muscle, with hypermetabolic right axillary level I lymph nodes, but no distant bone or visceral metastases. The stage was updated to locally advanced T4N++M0 disease. She began taxane/carboplatin chemotherapy, with a plan for 16 neoadjuvant sessions. Follow-up MRI and PET in May 2023 showed a partial but important response: the right breast tumor process, skin thickening, and axillary nodal disease all decreased, and the right breast had an almost complete morpho-metabolic response with only a small residual hypermetabolic area. Surgery on 19 May 2023 included right modified radical mastectomy with axillary lymph node dissection and left subcutaneous mastectomy with sentinel lymph node dissection. Three of 9 right axillary nodes were positive, so radiotherapy was added after surgery along with adjuvant chemotherapy. As of April 2025, she had responded well to multimodality treatment, with improved quality of life after an emotionally and physically difficult course.