ESTRO 36 Abstract Book

S319 ESTRO 36 _______________________________________________________________________________________________

Material and Methods The study population consisted of 931 previously untreated, biopsy-proven, and no distant metastasis NPC patients who finished curative radiotherapy with/without chemotherapy at our department. The pre-treatment pEBV DNA level was measured by the real-time quantitative polymerase chain reaction. We analyzed the relationship between the pEBV DNA status and clinical characteristics. Various survival curves were compared between the patients with detectable and undetectable pEBV DNA by the Kaplan-Meier method. Results EBV DNA signal (> 0 copies/mL) was detected in 90.8% (845/931) NPC patients’ plasma before treatment. The percentages in patents with undetectable EBV DNA were inversely associated with presenting stages (24.6% for stage I/II, 8.5% for stage III and 2.8% for stage IV, P<0.001). The pEBV DNA levels were positively correlated with clinical stage (P<0.001). The age, gender, and pathological type between the patients with detectable and undetectable pre-treatment pEBV DNA were similar. However, patients with detectable pre-treatment pEBV DNA had relatively poor performance status, advanced T- classification, advanced N-classification, and advanced overall stage than those with undetectable pEBV DNA. The overall survival (HR=0.4413, 95% CI = 0.29-0.67, P=0.0004, 10-year rate = 62.2% vs. 90.3%), neck failure-free survival (HR=0.3285, 95% CI = 0.12-0.93, P=0.0397, 10-year rate = 94.4% vs. 100%), and distant metastasis-free survival (HR=0.3751, 95% CI = 0.23-0.62, P=0.0002, 10-year rate = 79.9% vs. 97.7%) were significantly lower in patients with detectable pEBV DNA than in those with undetectable pEBV DNA. The local failure-free survival was similar between both subgroups (HR=0.8740, 95% CI = 0.46-1.67, P=0.9362, 10-year rate = 85.6% vs. 89.2%). Conclusion NPC patients presented with detectable pEBV DNA before treatment were associated with higher clinical stages and significant worse survivals. PO-0612 Significance of co-expression of mutant p53 protein and Ki67 in locally advanced HNSCC post chemo- RT P. Baskaran Shanmuga 1 , K. Periasamy 1 , S. Sharma 2 , G.K. Singh 1 , V. Yadav 1 , A. Gupta 1 , J. Kaur 1 , A.K. Mandal 2 , K.T. Bhowmik 1 1 Safdarjung Hospital, Radiotherapy, New Delhi, India 2 Safdarjung Hospital, Pathology, New Delhi, India Purpose or Objective To know the significance of the co-expression of mutant p53 protein and Ki67 in locally advanced HNSCC with respect to response to chemoradiation (CRT) and locoregional failure (LRF), distant metastasis (DM) and overall survival (OS) at 1 year. Material and Methods This prospective observational study included 62 patients with stage III-IV non nasopharyngeal HNSCC of which 58 patients completed CRT. Immunohistochemistry was done on the pre-treatment biopsy specimens and the expression of p53 and Ki67 in the tumor were graded based on the degree of nuclear staining. During statistical analysis, patients having co-expression (p53+/Ki67+) were categorised in one group and the rest in the non-co- expressed group (p53-/Ki67-, p53+/Ki67-, p53-/Ki67+). The patients were followed up for a minimum period of 1 year and the association between the co-expression of the markers and the tumor response to CRT and LRF, DM and OS at 1 year were analysed. Results 57% (33) patients showed co-expression of mutant p53 and Ki67 while 43% (25) patients fell in the non-co-expressed group. There was a statistically significant association between the co-expression of the markers and the parameters such as age <50 years, N2 stage, TNM stage IVA

and partial response(PR) to CRT at 8 weeks. Similarly, at 1 year, the absence of co-expression was associated significantly with the locoregional control of the disease while the presence was associated with LRF. Even though 8/9 patients with DM showed co-expression, a statistically significant association was not reached on analysis (p-value 0.064). The relative risk of PR and LRF were 4.16 and 3.59 respectively with p53 and Ki67 co- expression. On multivariate analysis, the co-expression of the markers was found to be a statistically significant independent predicting factor for PR at 8 weeks post CRT and LRF at 1 year with odds ratio 10.50 and 7.12 respectively, however, the N2 stage was a statistically significant independent factor of DM and mortality at 1 year with odds ratio of 6.16 and 11.14 respectively.

Conclusion These results signify that the co-expression of mutant p53 and Ki67 has specific role in the clinical course of locally advanced HNSCC, significant in predicting PR response to CRT and LRF at 1 year. Advanced Nodal stage (N2) has emerged as an independent predictor for DM and mortality at 1 year. PO-0613 Effect of geometric GTV-CTV margins in national contouring guidelines C.R. Hansen 1,2 , J. Johansen 3 , E. Samsøe 4 , E. Andersen 5 , J.B. Petersen 6 , K. Jensen 7 , H.M.B. Sand 8 , L.J. Andersen 8 , C. Grau 7 1 Odense University Hospital, Laboratory of Radiation Physics, Odense, Denmark 2 University of Southern Denmark, Faculty of Health Sciences, Odense, Denmark 3 Odense University Hospital, Department of Oncology, Odense, Denmark 4 University Hospital Herlev, Radiotherapy Research Unit- Department of Oncology, Herlev, Denmark 5 University Hospital Herlev, Department of Oncology, Herlev, Denmark 6 Aarhus University Hospital, Department of Medical Physics, Aarhus, Denmark 7 Aarhus University Hospital, Department of Oncology, Aarhus, Denmark