Abstract PO3-17-10: Real-World evidence for Pembrolizumab-based neoadjuvant chemotherapy in early-stage triple negative breast cancer: a single institution experience

Abstract Introduction The improved pathologic complete response (pCR) and event-free survival observed in Keynote-522 trial (NCT03036488) led to the adoption of (neo)adjuvant pembrolizumab (pembro)-based chemotherapy (CT) for high-risk early-stage triple-negative breast cancer (eTNBC) in various jurisdictions. However, Real-World Evidence (RWE) for (neo)adjuvant pembro in this setting would further support its ongoing funding and utilization. The aim of this study was to provide RWE for (neo)adjuvant pembro in eTNBC in the United Arab Emirates (UAE), where patients often present with more-advanced disease stages and poorer prognostic profiles compared with North America and Europe. Method This is a retrospective cohort study involving all patients treated with pembro-based neoadjuvant chemotherapy (NACT) for eTNBC at a major cancer center (Tawam Hospital) in the UAE between October 2021 and June 2023. Patient characteristics, clinicopathologic features, immune related adverse events (irAE) and disease outcomes were reported by descriptive statistics. An exploratory analysis was also conducted to examine the associations between pCR and HER-2 status (HER2 negative vs HER2 low) as well pCR and treatment interruption ( vs = 2 weeks). ResultA total of 41 patients, with a median age of 44 years, were included in this study. All had an ECOG status of 0-1. The clinical and pathological characteristics are provided in Table 1. Pathogenic germline BRCA (gBRCA) mutations were detected in 8 (21%) of the 38 patients who underwent testing, including 6 with gBRCA1 and 2 with gBRCA2), with additional TP53 and SMARC4 detected in one patient each. Approximately 66% of the patients (n = 27) completed surgery post neoadjuvant pembro+CT, of whom 18 (67%) had breast conserving surgery and 9 (33%) had mastectomy. Of the patients who underwent surgery, 60% (n = 16/27) achieved pCR including 68% (13/19) of the IHC 0+ and 37.5% (3/8) of the HER2 1+ or 2+ ISH negative (p-value = 0.429, Chi Square test). Of the total population, 16 (40%) did not complete NACT; 1 lost to follow-up, 9 were still on ongoing therapy, 2 discontinued therapy due to toxicity, and 4 developed progressions including 1 locoregional relapse, and 3 metastatic diseases. Of the 32 patients who completed at least 3 months of pembro-NACT, 14 (34%) reported any grade irAE: skin toxicity (N = 3, 21%), hypothyroidism (N = 8, 57%), Hyperthyroidism (N = 1, 7%), Hepatitis (N = 4, 28.5%), adrenal insufficiency (N = 1, 7%), and pneumonitis (N = 1, 7%). With a median follow up of 4.5 months, pembro was postponed in 4 patients and permanently discontinued in 1 secondary to severe pneumonitis requiring ICU admission. All irARs were graded at I and II, except for 1 grade III dermatitis, and 1 grade III pneumonitis. Interruption of IO was required for irAE in 5 (36%) patients, and steroids were administered in 4 (29%). pCR was observed in 6 (40%) patients out of 15 who experienced treatment interruption due to IrAE or CT and 10 out of 13 (77%) in those who did not experience treatment interruption (p = 0.04895, Chi-square test). Conclusion The pCR rates for Pembro-based NACT in this RWE study, involving patients with an overall higher risk disease, appeared to be consistent with those observed in keynote-522. Interestingly, pCR rates did not seem to differ between HER2 negative and HER2 low groups. However, pCR rates appeared to be lower in patients who experienced treatment interruptions. Approximately half of the patients developed irAE but the majority of the adverse events were of lower grade and did not require treatment interruptions. Overall, the RWE observed in this study supports the ongoing funding and utilization of Pembro-based NACT in eTNBC. Updated data, including the pCR rate and toxicity, will be presented at the meeting once most of the patients have completed surgery. Table 1: Clinical and Pathological Characteristics of patients (Nf41) XX- XX Citation Format: Aydah Al-Awadhi, Mouza AlShebli, Lina Wahba, Tallal Younis. Real-World evidence for Pembrolizumab-based neoadjuvant chemotherapy in early-stage triple negative breast cancer: a single institution experience abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-17-10.