Adjuvant immunotherapy following upfront surgery for stage II–III triple-negative breast cancer: A National Cancer Database Study.

e12520 Background: In early-stage triple-negative breast cancer (TNBC), immunotherapy (IO) improves outcomes when administered with chemotherapy in the neoadjuvant setting, with standard post-operative continuation. For patients undergoing upfront surgery, the benefit of adjuvant-only IO remains uncertain. IMpassion030 demonstrated no benefit from adding adjuvant atezolizumab after upfront surgery; the benefit of adjuvant-only pembrolizumab remains unclear, with SWOG 1418 pending. We leveraged a large national database to evaluate real-world outcomes. Methods: Using the 2022 National Cancer Database (NCDB), we identified patients with pathologic stage II–III TNBC diagnosed between 2015 and 2020 who underwent upfront surgery. Patients receiving neoadjuvant systemic therapy or preoperative radiation were excluded. Overall survival (OS) was calculated from diagnosis to last contact or death. Survival was compared between adjuvant chemotherapy alone versus chemotherapy + IO (captured as categorical variable in NCDB) using Kaplan–Meier methods and log-rank testing, stratified by pathologic stage. Stage-stratified analyses were univariate. Results: Among n=13,961 included patients, 11,805 had stage II and 1,835 had stage III disease. Of these, 98.5% (13,749) received adjuvant chemotherapy alone and 1.5% (212) received adjuvant chemotherapy + IO. There was no difference in median age (59 vs 59 years; p=0.85); race (White: 70.3% vs 71.6%; Black: 24.3% vs 19.9%; p=0.068); comorbidities (Charlson–Deyo score 0: 80.7% vs 81.6%; p=0.38) between chemotherapy vs. chemotherapy + IO groups. More patients with stage III disease received chemotherapy + IO (stage III: 24.5% vs. 13.4%; stage II: 85.9% vs. 73.6%, p<0.001). Landmark OS at 36, 60, and 96 months for chemotherapy alone versus chemotherapy + IO was 86.0% vs 83.2%, 79.7% vs 74.8%, and 73.3% vs 72.4%, respectively (log-rank p=0.17). There was higher survival rate among those with stage III disease who received chemotherapy vs. chemotherapy + IO, although not statistically significant. Conclusions: In this real-world cohort of patients with stage II–III TNBC treated with upfront surgery and adjuvant chemotherapy, the addition of IO was not associated with improved OS. These findings align with recently reported prospective trials and reinforce ongoing uncertainty regarding the benefit of adjuvant-only IO, underscoring continued prioritization of neoadjuvant approaches. Results from SWOG S1418 will further clarify this question. Overall survival by treatment and pathologic stage. Chemo Chemo + IO Stage II N 11,805 156 Events, n (%) 1,994 (17) 23 (15) Median OS, months (95% CI) NR NR OS 36 months, % 90.0 89.8 OS 60 months, % 83.9 83.4 OS 96 months, % 77.1 80.7 Stage III N 1,835 52 Events, n (%) 781 (43) 24 (46) Median OS, months (95% CI) 91.7 (79.8–NR) 54.7 (45.0–NR) OS 36 months, % 70.9 68.5 OS 60 months, % 58.4 49.2 OS 96 months, % 49.2 44.3 NR, not reached.