Poster Presentation Clinical Oncology Society of Australia Annual Scientific Meeting 2026

Complete responses to first-line pembrolizumab plus chemotherapy in PD-L1-positive advanced triple-negative breast cancer: a CEBCC-101 analysis (146005)

Małgorzata Podskarbi 1 , Agnieszka Pietruszka 2 , Małgorzata Pieniążek 3 4 , Miloš Holánek 5 6 , Aleksandra Konieczna 7 , Renata Pacholczak-Madej 8 9 , Zuzana Bielčiková 10 , Mirosława Püsküllüoğlu 2
  1. Oncology Department, Pleszew Medical Cente, Pleszew, Poland
  2. Department of Clinical Oncology, The Maria Skłodowska-Curie National Research Institute of Oncology, Kraków Branch , Kraków, Poland
  3. Lower Silesian Comprehensive Cancer Center, Wroclaw, Poland
  4. Department of Oncology, Wroclaw Medical University, Wrocław, Poland
  5. Department of Comprehensive Cancer Care, Masaryk University, Brno, Czech Republic
  6. Department of Comprehensive Cancer Care, Faculty of Medicine, Masaryk University, Brno, Czech Republic
  7. Department of Breast Cancer and Reconstructive Surgery, Maria Sklodowska-Curie National Research Institute of Oncology, Warsaw, Poland
  8. Department of Gynecological Oncology, The Maria Skłodowska-Curie National Research Institute of Oncology, Kraków Branch, Kraków, Poland
  9. Department of Anatomy, Jagiellonian University Medical College, Krakow, Poland
  10. Department of Oncology, First Faculty of Medicine, Charles University and General University Hospital, Prague, Czech Republic

Background: Complete responses (CRs) occur in a minority of patients receiving first-line pembrolizumab plus chemotherapy (P+C) for advanced triple-negative breast cancer (TNBC), and their optimal management remains undefined.

Methods: CEBCC-101 is a multicentre retrospective cohort of 178 patients from Poland, Slovakia and Czech republic with PD-L1-positive advanced TNBC treated with first-line P+C. Patients with investigator-assessed CR by RECIST v1.1 were identified. The first documented CR date was used to calculate time to CR and post-CR follow-up. Clinical features, treatment exposure, toxicity, management, progression, and survival were summarised descriptively.

Results: CR was documented in 8/178 patients (4.5%). Median age was 57.1 years; seven had ECOG performance status 1, and five had de novo metastatic disease. All had one or two metastatic sites; five had visceral disease and none had brain metastases. Median CPS was 25 (range, 12–100). Six patients received gemcitabine–carboplatin and two taxane-based chemotherapy. Median time to CR was 4.9 months (range, 2.7–10.7). Median chemotherapy and pembrolizumab exposure were 7.0 and 11.0 months; treatment remained ongoing in two and four patients, respectively. Grade 3–4 adverse events occurred in six patients, and three required chemotherapy dose reductions >20%. One patient progressed 21.1 months after CR; the other seven had no documented progression after a median post-CR follow-up of 7.1 months (range, 2.4–15.6). One patient underwent breast surgery after radiological CR and achieved ypT0N0. All were alive at data cut-off.

Conclusions: CR occurred in a small subset, often with de novo but limited-site metastatic disease, and was maintained in most despite frequent grade 3–4 toxicity and treatment modification. The observed rate was lower than the 17% reported in KEYNOTE-355 for CPS ≥10, although response ascertainment differed. Larger datasets are needed to identify predictors of CR and define the role of local surgery and optimal treatment duration after CR.