Real-world eligibility for perioperative pembrolizumab in resectable locally advanced head and neck squamous cell carcinoma: A SEER-based analysis following KEYNOTE-689.

e18059 Background: KEYNOTE-689 demonstrated improved outcomes with perioperative pembrolizumab added to standard multimodality therapy in resectable, locally advanced head and neck squamous cell carcinoma(HNSCC). However, the real world proportion of patients who meet KEYNOTE-689 eligibility criteria remains unclear. We evaluated real-world patient characteristics and treatment patterns to estimate eligibility for perioperative pembrolizumab. Methods: We performed a retrospective cohort analysis using the SEER 17 registries database (2017-2021). Adults diagnosed with stage III-IVB (locally advanced, non metastatic) HNSCC were identified using ICD-O-3 histology and primary site codes. Patients were stratified by derived EOD 2018 stage groups (III, IVA, IVB) and age (<60, 60-69, ≥70 years). Treatment patterns were assessed using SEER radiation and chemotherapy recode variables to characterize real world multimodality therapy consistent with KEYNOTE-689 clinical context. Descriptive analyses were performed. Results: A total of 9,135 patients with stage III-IVB HNSCC were identified. Stage distribution included 3,281 (35.9%) stage III, 3,439 (37.7%) stage IVB disease. Across all stages, patients were distributed across age groups, including many aged ≥70 years. Definitive radiation therapy was commonly delivered, with 7270 patients (79.6%) receiving beam radiation across all stage groups. Systemic therapy use was also frequent, with 6197 patients (67.9%) receiving chemotherapy, reflecting routine multimodality treatment patterns seen in everyday clinical practice. A smaller subset of patients declined or did not receive radiation or chemotherapy, reflecting real world limitations that may affect the ability to meet clinical trial treatment requirements. Conclusions: In a large U.S. population, many patients with locally advanced HNSCC have stage, age, and treatment characteristics similar to those included in KEYNOTE-689. These findings suggest that a meaningful number of real world patients could be considered for perioperative pembrolizumab. Further work is needed to better understand and address gaps between clinical trial criteria and treatment delivered in routine practice. Key characteristics and treatment patterns in locally advanced HNSCC (SEER 2017-2021). Variable Number (%) Stage III- IVB Stage III- 3,281(35.9), Stage IVA- 3,439 (37.7), Stage IVB- 1,562 (17.1) Age ≥ 70 years 2,487 (27.2%) Beam radiation received 7,270 (79.6%) Chemotherapy received 6,197 (67.9%)