[A Case Report of Triple-Negative Breast Cancer with High Ki-67 Expression That Responded to Neoadjuvant Pembrolizumab Therapy].

Drug therapy including pembrolizumab is expected to improve treatment outcomes for triple-negative breast cancer (TNBC). We experienced a case of early-stage TNBC with high Ki-67 expression and a high risk of recurrence, in which neoadjuvant pembrolizumab therapy was effective. A 72-year-old woman with TNBC who developed secondary adrenal insufficiency due to hypopituitarism during pembrolizumab treatment. Symptoms rapidly improved with steroid replacement therapy, pembrolizumab was discontinued. Later, the patient had experienced severe infections during subsequent chemotherapy but recovered, and underwent partial mastectomy. Pathological findings showed treatment effect Grade 1a with negative margins. Seven months later, she has shown no signs of recurrence. We report a case of TNBC with high Ki-67 expression that responded well to neoadjuvant pembrolizumab therapy.