Combining Pembrolizumab and Ofatumumab in Triple-Negative Breast Cancer and Multiple Sclerosis: A Case Report.

INTRODUCTION: Pembrolizumab has been widely used since its approval as perioperative therapy for triple-negative breast cancer. While the emergence of diverse antibody drugs has expanded therapeutic options in recent years, reports on the combined use of immune-related antibodies in patients with other diseases remain limited. CASE PRESENTATION: A 42-year-old woman presented with a 5-cm mass in her right breast. Needle biopsy confirmed invasive ductal carcinoma (cT2N0M0, cStage IIB, triple-negative breast cancer). Pembrolizumab-based therapy was considered, but the patient was already receiving ofatumumab, an anti-CD20 antibody, for multiple sclerosis (MS). After consultation with a neurologist, she underwent neoadjuvant chemotherapy with paclitaxel, carboplatin, and pembrolizumab, followed by epirubicin, cyclophosphamide, and pembrolizumab. Preoperative imaging indicated a clinical complete response. She underwent right partial mastectomy with sentinel lymph node biopsy, and postoperative pathology confirmed a pathologic complete response. No exacerbation of MS has been observed to date. CONCLUSIONS: This case demonstrates that pembrolizumab can be safely administered for triple-negative breast cancer in a patient receiving ofatumumab for MS, achieving a pathologic complete response.