Abstract PS4-07-12: Real-world comparison of pembrolizumab dosing schedules (q3w vs q6w) in early TNBC: Insights from the PETRHA cohort

Abstract Pembrolizumab combined with neoadjuvant chemotherapy has become the standard of care for most patients with early-stage triple-negative breast cancer (TNBC), typically administered at a dose of 200 mg every three weeks (q3w), as studied in the KEYNOTE-522 trial. A 400 mg every six weeks (q6w) dosing schedule was subsequently approved by regulatory agencies based on pharmacokinetic modeling and exposure-response analyses demonstrating comparable drug exposure and similar expected efficacy and safety to the standard q3w regimen. Although the q6w schedule was not evaluated in prospective neoadjuvant trials, its adoption has increased in real-world practice, particularly in settings with logistical constraints. However, comparative clinical data on the safety and efficacy of q6w versus q3w dosing in early TNBC remain limited. Patients with early TNBC who received neoadjuvant chemotherapy and pembrolizumab within the PETRHA retrospective cohort were included. Pembrolizumab was administered either 200 mg every three weeks (q3w) or 400 mg every six weeks (q6w), based on physicians' choice and local practice. Patients receiving q3w and q6w dosing were compared in terms of treatment completion (defined as receipt of all planned neoadjuvant pembrolizumab cycles), immune-related adverse events (irAEs), and pathologic complete response (pCR) rates, defined as ypT0/is ypN0. Descriptive statistics were used to summarize baseline characteristics. Categorical variables were compared using chi-square or Fisher’s exact tests. A two-sided p-value