Background Locally advanced head and neck squamous cell carcinomas (HNSCC) are treated with multidisciplinary approach which includes radiation therapy. Immunotherapy with nivolumab or pembrolizumab is used for platinum refractory disease. We analyzed the association of radiation treatment patterns and immunotherapy responses HNSCC.

Methods We performed a retrospective analysis at University of New Mexico Comprehensive Cancer Center for patients with diagnosis of HNSCC treated at our institution between 2011 and 2020 with immunotherapy agent’s nivolumab and pembrolizumab. Our cohort included 21 patients with previous history of definitive radiation therapy for HNSCC who received immunotherapy for recurrent disease, as part of adjuvant treatment as either front-line or second line therapy. In terms of response, patients were divided into responders (R) and non-responders (NR). Responders were defined as the presence of partial remission in initial imaging or stable disease for a period of six months or longer.

Results Of our 21 patients, 10 patients were R and 11 patients were NR. p16 positivity was 6 (60%) in R vs 3 (27%) in NR. 8 patients in R group (80%) and 10 patients in NR group (91%) had prior platinum based chemotherapy concurrent with radiation or for recurrence as salvage chemotherapy.All patients had radiation therapy prior to immunotherapy for adjuvant or for definitive treatment. Time from last day of radiation treatment to start of immunotherapy was 47 months in R group while it was 9 months in NR group (P<0.05). (Figure 1) There was no difference in time from radiation to immunotherapy depending on the P16 status. Immunotherapy was stopped after completing 2 years of immunotherapy for 3 patients. 2 of those patients resumed immunotherapy due to progression, and continue to have response after resuming treatment. One of these patients received SBRT to lung nodule after resuming immunotherapy.

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Abstract 462 Figure 1

Time from last day of radiation treatment to start of immunotherapy

Conclusions Immunotherapy with single agent PD-L1 inhibitor is used for platinum refractory disease in HNSCC, however response rates are low. Our study shows that the patients who had early recurrence and received immunotherapy closer to definitive radiation therapy had lower response rate. Therefore we need further studies to investigate changes in immune micorenvironment with radiation therapy for better immune targeting of patients with early recurrence after radiation treatment.