Abstract
Neoadjuvant chemoimmunotherapy with pembrolizumab now defines the standard of care for early high-risk triple-negative breast cancer (TNBC). However, the role of pembrolizumab in neoadjuvant therapy (NAT) for estrogen receptor-positive (ER+) breast cancer remains uncertain. A 39-year-old G2P2 female discovered a palpable mass in the right breast while breastfeeding her 7-month-old child, leading to the diagnosis of a high-grade ER+ (80% moderate staining), human epidermal growth factor receptor 2-negative (ErbB2-) invasive ductal carcinoma with axillary nodal involvement. Gene expression profiling with the MammaPrint 70-gene signature and BluePrint 80-gene signature revealed a tumor with high-risk, basal-type biology. The multidisciplinary breast cancer team recommended NAT with pembrolizumab, carboplatin, paclitaxel, doxorubicin, and cyclophosphamide. Within six weeks, the patient exhibited a remarkable response, with no palpable mass or lymph node, and post-treatment examinations confirmed a complete clinical and radiologic response. The patient underwent lumpectomy and sentinel lymph node biopsy, revealing a pathological complete response with minimal ductal carcinoma in situ and negative axillary nodes. Adjuvant radiation therapy was administered, and the patient completed adjuvant pembrolizumab, currently showing no evidence of recurrence. This case underscores the potential benefits of neoadjuvant chemoimmunotherapy for patients with ER+ErbB2- high-risk, basal-type breast cancer. The use of immunotherapy in patients with pregnancy-associated breast cancer remains to be further investigated.