ESTRO 36 Abstract Book

S264 ESTRO 36 2017 _______________________________________________________________________________________________

current TNM for NPC, failure patterns, and outcomes were compared between OPC and NPC. Results A total of 802 HPV+ OPC and 369 NPC (360 EBER+ and 9 HPV+) were eligible. Compared to NPC, OPC were older (median age: 59 vs 52), and comprised more males (83% vs 67%), Caucasians (94% vs 20%; Asian 4% vs 75%), smokers (66% vs 40%), and drinkers (35% vs 9%) (all p<0.01). OPC presented more often as T1-T2 (58% vs 43%), and/or unilateral neck diseases (57% vs 24%) (all p<0.01). Median follow up was 4.5 years for OPC and 6.1 years for NPC. Distant metastasis (DM) was the main form of failure for both diseases and occurred in 92 (11%) OPC and 51 (14%) NPC patients. Most DM (85% OPC and 76% NPC) did not have local or regional failures (p=0.22). DM to multiple sites was common for both (51% OPC DM and 35% NPC DM) and most commonly to lung, liver, and bone for both. However, DM to brain was more often in OPC vs NPC (13% vs 2%, p=0.03). Compared to NPC, OPC had slightly higher 5-year recurrence-free survival (RFS) (84% vs 79%, p=0.01) but became non-significant after adjusting for TNM (HR 0.89, p=0.40). RFS for OPC was higher in T1 (93% vs 88%, p=0.045) or N0 (91% vs 78%, p=0.047), but similar for T2 (88% vs 80%, p=0.13), T3 (80% vs 81%, p=0.76), T4 (68% vs 62%, p=0.61), N1 (88% vs 82%, p=0.09), N2 (77% vs 81%, p=0.66), and N3 (67% vs 60%, p=0.75) diseases. Similar RFS was found for the HPV+ OPC specific TNM (ICON-S) stage I and current NPC I-II [both T1-2N0-1] (91% vs 90%, p=0.26), OPC ICON-S II vs NPC III [both T1-2N2 or T3N0-2] (84% vs 87%, p=0.95), and OPC ICON-S III vs NPC IVA-B [both T4 or N3] (69% vs 63%, p=0.56). Long-term survivors (survived >2 years after DM) were found in 24/92 (26%) OPC and 15/51 (29%) NPC with DM. Overall survival after DM for OPC and NPC were also similar (5-year: 17% vs 22%, p=0.20). Conclusion This large western cohort study depicted remarkable similarity with few differences in clinical presentation and outcomes between viral related OPC and NPC in the IMRT era. Patterns of relapse and oncologic outcomes are very similar by TNM classification. DM is the main form of failure and long-term survivors after DM are seen for both diseases. Such similarities in clinical behavior could reflect common mechanisms of oncogenesis, metastasis, and radio-/chemo- sensitivity and/or resistance induced by HPV and EBV. Uncovering these pathways could present new therapeutic opportunities for both diseases in the future. PV-0507 NGS for prognostic stratification in oral cancer harboring lymph node without extracapsular spread H.M. Wang 1 , C.T. Liao 2 , T.C. Yen 3 , S.J. Chen 4 , L.Y. Lee 5 , C.H. Hsieh 1 , C.Y. Lin 6 , S.H. Ng 7 1 Chang Gung Memorial Hospital, Division of medical oncology- Department of internal medicine, Taoyuan, Taiwan 2 Chang Gung Memorial Hospital, Section of Head and Neck Surgery- Department of Otorhinolaryngology, Taoyuan, Taiwan 3 Chang Gung Memorial Hospital, Department of Nuclear Medicine and Molecular Imaging Center, Taoyuan, Taiwan 4 ACT Genomics, Taipei, Taiwan 5 Chang Gung Memorial Hospital, Department of Pathology, Taoyuan, Taiwan 6 Chang Gung Memorial Hospital, Department of Radiation Oncology, Taoyuan, Taiwan 7 Chang Gung Memorial Hospital, Department of Diagnostic Radiology, Taoyuan, Taiwan Purpose or Objective Patients with resected oral squamous cell carcinoma (OSCC) harboring metastatic lymph node without extracapsular spread (ECS) show heterogeneous outcomes. We aim to improve their prognostic

stratification traditional clinicopathological prognosticators with the genetic information obtained from next-generation sequencing (NGS). Material and Methods The hotspot mutation regions of 45 cancer-related genes were investigated using NGS with an ultra-deep (>1000×) sequencing approach in formalin-fixed paraffin-embedded samples obtained from 144 patients who had resected OSCC harboring neck lymph node without ECS. Results Pathologic T4 was the most important traditional prognosticators for disease-specific survival (DSS). The 5- year DSS for patients with pT4 versus pT1-3 was 48.8% versus 80.2% (P < 0.001). Multivariate analysis in patients with pT1-3 (n = 101) identified the following adverse prognostic factors: 1) HRAS/BRAF mutation (n = 7) for distant metastasis (DM) (27% versus 7%, P = 0.006) and DSS (57% versus 82%, P = 0.005); and 2) TP53 DNA-binding domain missense mutations (n = 38) for DM (13% versus 3%, P = 0.053) and DSS (68% versus 90%, P = 0.004). The prognosticators in patients with pT4 (n = 43) were: 1) Lymph node number ≥3 (n = 10) for locoregional failure (70% versus 33%, P = 0.032) and DSS (30% versus 55%, P = 0.050); 2) HRAS/BRAF mutation (n = 6) for DM (67% versus 14%, P = 0.008) and DSS (0% versus 57%, P = 0.001); and 3) no adjuvant radiotherapy (n = 2) for DSS (0 versus 51%, P = 0.013). Conclusion Genetic information from NGS may improve the prognostic stratification offered by traditional prognosticators in resected OSCC patients harboring metastatic lymph node without ECS. Our findings will contribute to implementation of precision medicine in OSCC patients. PV-0508 Prognostic significance of PD-L1 expression in patients with head and neck squamous cell carcinoma C. Peng 1 , X. Gu 1 , X.S. Gao 1 , X. Li 1 , S. Qin 1 , M. Ma 1 , M. Cui 1 , M. Xie 1 , Y. Bai 1 1 Peking University First Hospital, Department of Radiation Oncology, Beijing, China Purpose or Objective Previous studies have investigated the association between programmed death ligand-1 (PD-L1) expression and survival of patients with head and neck squamous cell carcinoma (HNSCC). However, the results were controversial and inconclusive. We therefore conducted a meta-analysis of published studies to evaluate the prognostic significance of PD-L1 expression in HNSCC. Material and Methods Relevant studies were retrieved through PubMed, Web of Science, Embase, Cochrane Library, China National Knowledge Infrastructure (CNKI). Combined hazard ratio (HR) and 95% confidence interval (CI) were calculated to assess the association between PD-L1 and overall survival (OS), progression-free survival (PFS)/ disease-free survival (DFS), cancer-specific survival(CSS). ORs with 95% CIs were calculated to evaluate the relationship between PD-L1 status and clinicopathological factors. Subgroup analyses and publication bias were also conducted. Results A total of 12 studies (13 cohorts) with 1777 patients were ultimately included in the meta-analysis. Results showed that high PD-L1 expression predicted poor CSS in HNSCC (HR 1.472, 95%CI: 1.013-2.138). Stratification analyses revealed that high PD-L1 expression was associated with poor OS in Asians (HR= 1.301; 95% CI:1.056-1.602) and oral SCC (HR=1.343; 95% CI:1.071-1.685) patients. In addition, we observed that high PD-L1 expression was correlated with female patients (OR=0.638, 95% CI: 0.478-0.853), lymph node metastasis (OR=1.415, 95% CI: 1.082-1.85), nonsmokers (OR=0.753, 95% CI: 0.569-0.995), HPV positive patients (OR=1.523, 95% CI: 1.032-2.247) in HNSCC. by combining the