ESTRO 2021 Abstract Book

S840

ESTRO 2021

Conclusion Careful accumulation of dose to OAR demonstrated association between cumulative dose and carotid blowout even for this limited cohort and the results support the existing dose constraint for the carotid arteries of 120 Gy. PO-1011 Efficacy of PD-1 inhibition in recurrent Head and Neck cancer. A national prospective cohort study. S. Søby 1 , A. Gothelf 2 , N. Gyldenkerne 3 , J. Bentzen 4 , K. Nowicka-Matus 5 , T. Tramm 6 , J.G. Eriksen 1 1 Aarhus University Hospital, Dept. of Experimental Clinical Oncology, Aarhus, Denmark; 2 Copenhagen University Hospital, Dept. of Oncology, Copenhagen, Denmark; 3 Odense University Hospital, Dept. of Oncology, Odense, Denmark; 4 Herlev Hospital, Dept. of Oncology, Copenhagen, Denmark; 5 Aalborg University Hospital, Dept. of Oncology, Aalborg, Denmark; 6 Aarhus University Hospital, Dept. of Pathology, Aarhus, Denmark Purpose or Objective PD-1 inhibitors are well established in the treatment of recurrent or metastatic head and neck squamous cell carcinoma (rmHNSCC). These data come from randomized trials in selected patient populations. Aim of the present study was to investigate real-life efficacy of PD-1 inhibitors among an unselected and unbiased national cohort of rmHNSCC to determine the actual benefit of this treatment after failure of radiotherapy. Materials and Methods Patients (pts) were eligible if they had histologically or radiologically confirmed rmHNSCC and were treated with a PD-1 inhibitor. Patient, tumor and treatment-related data were collected prospectively from patient files at the five head and neck cancer centers and from the DAHANCA-database. RECIST 1.1 was used for treatment evaluation. Descriptive statistics and parametric/non-parametric tests were used to describe patient, tumor and treatment characteristics. Endpoints were response rate (RR), overall survival (OS) and progression-free survival (PFS), calculated from start of treatment to date of event or censoring. Survival was estimated by the KM-method. All analyses were two-sided and p-values <0.05 were considered significant. Results In total 189 pts were identified between 2017 and 2020. Of these 136 (72 %) were male and 53 (28 %) female with a median age of 63 years [range 34-86]. 135 (71 %) had metastatic disease while 54 (29 %) were of the locally advanced type. The median number of treatment cycles administered was 4 [range 1-54]. The RR was 20%, median OS was 11.3 months [range 9.3-13.8] and the PFS was 5.8 months [range 4.2-9.2]. Pts with a PD-L1 expression <50 % (by any scoring method) seemed to have a lower OS than pts with a PD-L1 expression ≥50 % (p=0.04 HR=0.63 [95% CI: 0.40-0.99]). Disseminated vs. locally advanced disease did not affect outcome (p=0.7). OS was significantly correlated to WHO PS (p<0.0001, HR=3.0 [95% CI: 2.0-4.3]). Median OS was 21.1 months and median PFS was not reached within PS = 0. With PS = 1 median OS and PFS were 10.2 and 5.2 months respectively and 4.8 and 2.1 months for pts with PS ≥ 2. In contrast, elderly pts (≥ 70 years) had similar benefit as the younger pts (p=0.07), and no difference was found between genders (p=0.4). These data were also reflected using PFS as endpoint. Furthermore, OS and PFS were not significantly correlated to Charlson Comorbidity Score (p=0.1 resp.) Concomitant treatment of steroids was tested using OS as endpoint by comparing pts who had received concomitant steroids for ≥50 % of the duration of their PD-1 treatment time to pts who had received it for <50 % (p=0.004 HR=2.7 [95%CI: 1.3-5.3]). The same pattern was seen for PFS. Conclusion This national study showed acceptable efficacy in an un-selected cohort with one-fourth of pts surviving more than one year. However, around one-fourth has a rather rapid recurrence. Although a non-toxic treatment, response seems to be affected by poor performance and the need for steroid treatment during PD-1 therapy.