Background: Triple-negative breast cancer (TNBC) accounts for 15–20% of all breast cancer cases and is associated with the poorest prognosis among subtypes. The phase III KEYNOTE-522 trial evaluated the efficacy of neoadjuvant pembrolizumab combined with chemotherapy versus chemotherapy alone. It demonstrated a pathological complete response (pCR) rate of 64.8% in the pembrolizumab-chemotherapy group, compared to 51.2% in the control group. This study aims to look at real-world data from Northern Beaches Hospital, Sydney particularly concerning pCR and treatment tolerance.
Methods: We conducted a retrospective cohort study including all patients with early-stage TNBC treated with neoadjuvant pembrolizumab-chemotherapy from 2022 to April 2025. Eligible patients were managed at, or discussed in, the Northern Beaches Hospital breast multidisciplinary team (MDT). Inclusion criteria required patients to be over 18 years of age and to have completed surgery by April 2025.
Results: Fifteen patients met inclusion criteria, with a median age of 51 (range 42-63). 33% (5/15) patients had a germline BRCA 1 or 2 mutation detected. 5/15 patients (33%) achieved a pCR. Among the ten patients with residual disease, 2/10 (20%) had a Residual Cancer Burden (RCB) score of 1, 8/10 (80%) had an RCB score of 2, and 0/10 had an RCB score of 3. 2/15 patients (13%) developed metastatic recurrence during the study period. Adverse events and treatment adherence will be reported at COSA.
Conclusions: Real-world outcomes from Northern Beaches Hospital demonstrated a lower pCR rate (33%) compared to the 64.8% observed in the KEYNOTE-522 trial. This difference is likely influenced by the small sample size in our cohort. Nonetheless, the findings highlight the importance of ongoing real-world evaluation of immunotherapy-based regimens. Larger studies are needed to validate these results and explore potential factors contributing to variations in treatment response outside of clinical trial settings