ESTRO 2021 Abstract Book

S451

ESTRO 2021

SP-0571 Against the motion C. Parker 1 1 Royal Marsden Hospital, Uro-oncology, Sutton, United Kingdom

Abstract Text The main arguments against the routine use of rectal spacers in men having prostate radiotherapy are: 1. Prostate radiotherapy has a low risk of significant rectal toxicity. The typical risk of Grade 2 or worse late rectal toxicity is around 2%. There is therefore limited scope for improvement. 2. The evidence that rectal spacers reduce toxicity is weak. The case for rectal spacers is largely based on one randomised controlled trial that has numerous limitations. 3. Rectal spacers can cause catastrophic complications. Although not common, rectal spacers have led to severe complications such as pelvic abscesses and colostomies. 4. We need better evidence to determine the role of rectal spacers before they can be recommended as standard of care.

SP-0572 B. Vanneste The Netherlands

Abstract not available

SP-0573 C. Parker United Kingdom

Abstract not available

Symposium: New opportunities for radio-immunotherapy in head and neck cancer

SP-0575 Biological basis for radiotherapy combined with immunotherapy in head and neck PD1/PD-L1 E. Deutsch France

Abstract not available

SP-0576 PD-L1 expression and HPV in neck and head cancer: The rationales for a new treatment approach J.G. Eriksen 1 1 Aarhus University Hospital, Experimental Clinical Oncology, Aarhus, Denmark Abstract Text HPV/p16–positive oropharyngeal carcinomas, represent a biologically distinct subgroup of head and neck cancer. These tumours exhibit distinct immune characteristics and a different tumour microenvironment compared with HPV/p16-negative tumours. HPV/p16-positive oropharyngeal carcinomas have higher expression of PD-L1, a greater level of tumour infiltrating lymphocytes (TILs), such as T, B, and NK cells, compared with HPV/p16-negative tumours and patients whose HPV/p16-positive tumours have higher TIL levels have better outcome than those with lower TIL levels. This seems to some degree also to be influenced by the smoking status. Overall patients with HPV/p16-positive oropharyngeal carcinomas have a better prognosis and a dramatically improved five-year survival compared with their HPV/p16 -negative counterparts. Given the high survival rate, efforts have been made to de-intensify treatment. However, still without success. The lecture will discuss the current evidence and indications for PD-1 inhibitors in HPV/p16-positive oropharyngeal carcinomas and what information we need to identify a group that potentially benefit from immuno-radiotherapy instead of radiotherapy alone or chemo-radiotherapy and what we know about the type of radiation needed and the timing of radiotherapy. Emerging evidence for new approaches using HPV- vaccines and PD-1 inhibitors in the palliative setting will be reviewed. SP-0577 Combining radiotherapy and check point immune inhibitors in head and neck cancer: Preclinical and clinical approaches. K. Harrington 1 1 The Institute of Cancer Research, Radiotherapy and Imaging, London, United Kingdom Abstract Text There has been huge interest in the development of radiotherapy (RT)/chemo-radiotherapy (CRT) combinations with immunotherapy in a range of tumour types, including head and neck cancer (HNC). Initial trials have focussed on the use of anti-PD1/anti-PD-L1 immune checkpoint inhibition (ICPI) with RT/CRT, with a focus on using pre-RT loading, concomitant and post-RT adjuvant dosing. Recent data, however, have been negative (Javelin-100 Head and Neck, Pembro-Rad) and reports from forthcoming studies are awaited with great interest (e.g. KEYNOTE-412, ImVOKE-10, ComPARE). While questions about optimal scheduling of anti- PD1-based therapies remain, there is also a need to explore novel approaches that have the potential to