Abstract 842: Early clinical outcomes of pembrolizumab plus neoadjuvant chemotherapy in early stage triple negative breast cancer in a Hispanic majority community

Abstract Background: Triple-negative breast cancer (TNBC) accounts for 15% of breast cancers, and it has a poor prognosis with a five-year survival of 8 to 16% lower than that of hormone receptor-positive disease. There is a high prevalence of TNBC among Hispanics. In KEYNOTE-522 (KN522), a phase 3 trial, pembrolizumab plus neoadjuvant chemotherapy had been shown to be an effective option for pathological complete response (pCR) in early-stage TNBC as compared to neoadjuvant chemotherapy alone at the time of definitive surgery. While this treatment protocol showed promising data, immune checkpoint inhibitors such as pembrolizumab have been known to cause immune-related adverse effects (iRAEs) such as thyroiditis. There are limited studies on the efficacy of this treatment protocol and its adverse effects in Hispanic communities. Our study aims to present the relationship between pCR and immune-mediated thyroiditis in pembrolizumab plus neoadjuvant therapy for early-stage TNBC in a Hispanic-majority population in South Texas. Methods: This is a retrospective analysis of patients with stage II or III TNBC at Mays Cancer Center in San Antonio, Texas between January 2020 to November 2024. This KN522 treatment protocol included neoadjuvant therapy with four cycles of pembrolizumab every 3 weeks plus paclitaxel and carboplatin. Patients then received four additional cycles of pembrolizumab and doxorubicin-cyclophosphamide or epirubicin-cyclophosphamide. At the 24-week mark, patients were assessed to see if they had successfully completed the KN522 protocol as planned. Patients were assessed for pCR at the time of definitive surgery. Outcomes include assessing for the development of immune-mediated thyroiditis. Statistical analysis to compare outcomes between Hispanics and non-Hispanics was performed using R v4.2. Results: 66 patients were originally identified on review. 3 patients were excluded based on incomplete data. 63 patients were identified (68.3% Hispanic, 31.6% Non-Hispanic). At the time of definitive surgery, 55.6 % of patients had pCR (62.9% Hispanic, 37.1% Non-Hispanic) vs 44.4% with no pCR (75.0% Hispanic, 25.0% Non-Hispanic) with a p-value = 0.3. Comparing pCR and the development of immune-mediated thyroiditis, 14 patients with pCR (40%) vs 9 patients with no pCR (32.1%) developed immune-mediated thyroiditis with a p-value = 0.5. Conclusion: There was no difference in pCR with pembrolizumab plus neoadjuvant chemotherapy between Hispanic and non-Hispanic populations. Furthermore, there was no difference in pCR between patients who developed immune-mediated thyroiditis or not. Our results were notable for occurring in a Hispanic majority population, but our study was limited by a small sample size. More studies are needed with a larger sample size to ascertain if there is a difference in outcomes between Hispanic vs non-Hispanic patients. Citation Format: Aymen Baig, Erin C. Kaser, Nico-al Paolo Gotera, Jay Parekh, Ranjit S. Banwait, Marcela Mazo Canola. Early clinical outcomes of pembrolizumab plus neoadjuvant chemotherapy in early stage triple negative breast cancer in a Hispanic majority community [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 842.