Stage 3 breast cancer: pathologic complete response to neoadjuvant chemotherapy

What happened, in summary

This 39-year-old woman noticed a right breast lump while breastfeeding her 7-month-old baby in November 2022. Ultrasound showed 2 irregular hypoechoic lesions, including a breast mass and an abnormal axillary-tail lymph node. On examination, the breast was engorged from breastfeeding, with a large palpable upper-outer breast mass and a mobile axillary nodule. Biopsy showed Nottingham grade 3 invasive ductal carcinoma with marked atypia and very high proliferation. The breast tumor was ER 80% positive, PR 0%, HER2 0, and Ki-67 greater than 90%. The axillary node contained metastatic breast adenocarcinoma with weaker ER expression at 40%, PR 0%, and HER2 0. MRI showed a 5.8 cm breast mass and a single enlarged axillary node; PET/CT showed no distant metastasis. She was anatomically staged IIIA, cT3N1M0, with a reported prognostic stage of IIIB. Hereditary cancer testing was negative. Because MammaPrint showed high risk and BluePrint classified the tumor as basal-type, the tumor board treated the biology as closer to high-risk triple-negative disease. She received pembrolizumab with carboplatin and paclitaxel, followed by doxorubicin and cyclophosphamide, though she declined the fourth AC cycle because of profound fatigue. After 6 weeks, the mass and node were no longer palpable. Surgery included right lumpectomy, clipped-node removal, and sentinel node biopsy. Pathology showed only a 0.2 cm focus of DCIS, all 8 nodes were negative, and residual cancer burden was 0. She completed breast/regional-node radiation and adjuvant pembrolizumab and remained recurrence-free at last follow-up. The result was especially strong because the original tumor was large, node-positive, high-grade, and biologically basal-type despite estrogen receptor staining.