What happened, in summary

This 71-year-old woman, postmenopausal since age 50, came to the hospital in February 2024 with a left breast mass that had been present for more than 3 years. Examination found a hard, irregular 3.5 x 3 cm mass in the outer left breast, without palpable axillary lymph-node enlargement. Ultrasound and MRI showed suspicious left breast findings, and staging CT scans of the chest, abdomen, and pelvis did not identify another primary tumor site. On March 11, 2024, she underwent radical mastectomy for left breast cancer with sentinel lymph-node biopsy. Final pathology showed primary neuroendocrine carcinoma of the breast. The tumor was triple-negative: ER-negative, PR-negative, and HER2-negative. It also expressed neuroendocrine markers CgA, Syn, and CD56. Ki-67 was 30%, PD-L1 was positive with CPS at least 10, and genetic testing identified a germline BRCA1/2 mutation. The final pathologic stage was T2N0M0, Stage IIA. Because the tumor was rare, high-risk, triple-negative, PD-L1-positive, and BRCA-mutated, a multidisciplinary team recommended adjuvant chemotherapy combined with immunotherapy. She received paclitaxel 175 mg/m² and cisplatin 75 mg/m² on day 1 of each 21-day cycle, for a planned total of 6 cycles, together with pembrolizumab 200 mg every 3 weeks. She tolerated treatment well, with grade 1-2 myelosuppression, mild gastrointestinal symptoms, and peripheral nerve numbness, all managed supportively. No grade 3-4 serious adverse events occurred, and treatment was completed. Follow-up included physical exams, breast and regional lymph-node ultrasound, enhanced CT scans, and tumor markers. As of March 2025, 12 months after surgery, there was no local recurrence or distant metastasis.