Patterns and outcomes of palliative radiation therapy with immunotherapy in locally recurrent head and neck squamous cell carcinoma.

e18015 Background: Immune checkpoint inhibitors (ICI) have been shown to improve outcomes in patients with recurrent or metastatic (R/M) head and neck squamous cell carcinoma (HNSCC). Radiation therapy (RT) is commonly incorporated into R/M HNSCC treatment for symptom management and disease control. RT is a potential immunostimulatory treatment modality that may enhance the antitumor activity of ICI; however, ideal sequencing of RT and ICI in the palliative treatment setting is not defined. The objective of this study was to describe the patterns and outcomes of RT and ICI in locally recurrent HNSCC. Methods: All adults (≥ 18 years) with HNSCC who received palliative ICI for R/M disease from 2015-2021 were identified from the institutional electronic medical record via ICD codes under an IRB approved protocol. Patients who received ICI for non-HNSCC, had synchronous primary tumors, or had history of hematologic malignancy or immunodeficiency were excluded. Patients without documentation of clinical outcomes after palliative RT were excluded. Retrospective data were collected and underwent descriptive analysis. Results: We identified 26 patients who received palliative ICI and RT for locally recurrent HNSCC. Twelve underwent palliative RT while on ICI. In this group, there were 0 patients with complete response (CR), five with partial response (PR), two with stable disease (SD), and four with progression of disease (PD) in the target lesion. There were 10 grade 3 events. Fourteen patients had RT separately from ICI: 6 before and 8 after receiving ICI. In this group, there was one patient with CR, six with PR, one with SD, and six with PD in the target lesion. There were 3 grade 3 events. Most common grade 3 events in both groups were: dysphagia, mucositis, and voice change. The most common modalities of RT were SBRT, IMRT, and 3D conformal; 7 patients underwent SBRT, 19 underwent IMRT/3D conformal, with similar responses in target lesions. Conclusions: These data suggest that concurrent ICI and palliative RT for locally recurrent HNSCC is effective in the target lesions, but has an increase in toxicities. Although there was a small number of patients who underwent concurrent ICI and RT, the disease control rate (DCR) in this group was 58%, which is promising. Similarly, the DCR for patients receiving ICI and RT separately was 57%. Further study on the optimal type and sequence of palliative RT in this patient population is warranted.