ESTRO 2021 Abstract Book

S852

ESTRO 2021

Unit, IRCSS Azienda Ospedaliero-Universitaria di Bologna, Bologna, Italy; 3 Endocrinology Center, IRCSS Azienda Ospedaliero-Universitaria di Bologna, Bologna, Italy; 4 Radiation Oncology, IRCSS Azienda Ospedaliero- Universitaria di Bologna; Department of Experimental, Diagnostic and Specialty Medicine – DIMES - Alma Mater Studiorum Bologna University, Bologna, Italy; 5 Radiotherapy Department, Ospedale Bellaria, Bologna, Italy; 6 Department of Experimental, Diagnostic and Specialty Medicine - DIMES , Alma Mater Studiorum Bologna University, Bologna, Italy Purpose or Objective There is still lack of data in literature about the real 18FDG-PET/CT impact on treatment management in advanced and aggressive thyroid cancers. The first aim of our study was to retrospectively assess the impact of 18F-FDG PET/CT and secondly to confirm the prognostic role of clinical and semi-quantitative metabolic 18F-FDG PET/CT parameters in comparison with scientific literature. Materials and Methods A monocentric retrospective/observational study was performed from a database of 208 pts treated in our Center, from January 2011-July 2019, for local/metastatic DTC with several RAI courses. Fifty-three pts underwent 18FDG-PET/CT scan after the second RAI course because of strong suspect of RAI-R-DTC (negative Rx-WBS scan and/or high thyroglobulin levels). Clinical, laboratory and imaging data were collected. Metabolic response was defined according to PERCIST criteria. SUVmax, SUVmean, MTV, TLG were calculated. Kruskal- Wallis,Chi-Square-Pearson tests and Cox regression were used to compare metabolic/clinical parameters and PFS. Results In our sample (mean age: 52±19.9years; 31F-22M) 20/53 (38%) pts had negative RxWBS and positive PET/CT scan, 7/53 (13%) pts had positive RxWBS and PET/CT scans, 24/53 (45%) negative RxWBS and PET/CT scan and 2/53 (4%) positive RxWBS and negative PET/CT scan. Therapeutic approaches addressed after PET/CT positivity were external-beam-radiation therapy in 4/27(15%) pts, surgery in 4/27(15%), further RAI course in 2/27(7.4%), surgery+EBRT in 1/27(4%) and observation in 16/27(59%) pts. PERCIST response was evaluated in 14/27 FDG/PET positive scans. Median FU and median PFS were 5.8±3.9 years and 38±21.8 months respectively. At the last FU, 13/53 (24.5%) pts had persistence of structural disease, 25/53 (47%) persistence of biochemical disease and 15/53 (28%) excellent response. Significant associations were found between clinical response assessment and therapeutic approach (p=0.01) and between PFS and metabolic response (p=0.02). Linear correlation between MTV and TLG and suppressed-Tg was found. At Cox-Regression multivariate analysis only MTV (p=0.034 HR 1.100 CI95% 1.007-1.202) and PERCIST response (p=0.004 HR 2.434 CI95% 1.322-4.481) were independently associated to persistent disease. Conclusion Our analysis suggest that 18F-FDG-PET/CT may drive the clinical management of RAI-R-DTC, particularly to avoid further ineffective/toxic RAI administrations. PO-1024 Survival outcomes for p16+ oropharyngeal squamous cell carcinoma based on HPV status S. Robinson 1 , J. Towler 1 , R. Kitson 1 , D. Saleh 1 , H.C. Younan 1 , S. Mukhopadhyay 2 , J. Weir 2 , D. Gujral 1,3 1 Imperial College Healthcare Trust, Clinical Oncology, London, United Kingdom; 2 Imperial College Healthcare Trust, Histopathology, London, United Kingdom; 3 Imperial College, Department of Surgery and Cancer, London, United Kingdom Purpose or Objective Survival outcomes for HPV+ oropharyngeal cancer are favourable, leading to calls for treatment de-escalation. Internationally, HPV status is assessed by p16 immunohistochemistry (IHC), however UK guidance recommends an additional assessment of (high-risk) HPV DNA as a second-line molecular test. However, there is a degree of discordance between methods and there is controversy as to whether p16+/HPV+ and p16+/HPV- patients have equivalent prognosis. This clouds the identification of a favourable population suitable for de-escalation. In this single-centre retrospective analysis, we compare outcomes for p16+ patients treated radically at our institution from July 2010 to July 2018. Materials and Methods All p16+ patients were identified from our histopathology database. p16 status was assessed by IHC and HPV status (16 and 18) was assessed by DNA in situ hybridisation (DNA-ISH). Clinical demographic, tumour, treatment and survival data were collected from the electronic patient record. Differences were tested in SPSS using independent samples t-tests. Survival was taken from date of completing radiotherapy and analysed using the Kaplan-Meier method and compared using the log-rank test. Results We identified 132 eligible p16+ patients; 66% were HPV+ and 34% were HPV-. Patient demographics are shown in Table 1, with no significant difference between groups. Disease free survival at 5 years was 85% for HPV+ and 80% for HPV- as shown in Figure 1A (p=0.219), whilst overall survival at 5 years was 87% and 74% respectively (p=0.103), shown in Figure 1B. Whilst the survival curves start to separate after 3 years, this was not statistically significant.