ESTRO 2021 Abstract Book

S826

ESTRO 2021

taken to improve the NPC patients’ nutritional status during radiotherapy.

PO-0994 Correlation of PDL1-Tumor Infiltrating Lymphocytes in Carcinoma Oropharynx with toxicity & response S. Srivastava 1 , M. Rastogi 1 , A.K. Gandhi 1 , K. Sahni 1 , N. Husain 2 , R. Khurana 1 , R. Hadi 1 , S. Sapru 1 , S.P. Mishra 1 , A. Srivastava 1 , A. Bharati 1 , S. Parida 1 1 dr Rml Institute Of Medical Sciences, Radiation Oncology, Lucknow, India; 2 dr Rml Institute Of Medical Sciences, Pathology, Lucknow, India Purpose or Objective The Programmed Death Receptor Ligand 1 (PD-L1), is a cell-surface glycoprotein expressed in tumor cells (TCs) and is also up regulated in tumor infiltrating lymphocytes (TILs). The interaction of PD1 and PD-L1 can suppress the cytotoxic CD8 T-cell mediated immune response. Several studies have shown correlation of PD-L1 expression with tumor burden and survival in head and neck cancers, and its role as a valuable biomarker in predicting cancer prognosis, but studies evaluating the association between its expression in TILs and survival of cancer patients are limited. We intend to evaluate the correlation of toxicity and response with PD-L1 expression in TILs in oropharyngeal cancer patients receiving definitive chemo-radiation. Materials and Methods Our study was a prospective observational study in histopathologically proven squamous cell carcinoma of oropharynx with stage II-IVA (AJCC 8 th ) and Karnofsky performance status 70 or above. PDL1 expression in Tumor Infiltrating leucocytes (TILs) was assessed using immunohistochemistry technique. Definitive radiotherapy (RT) of 70 Gray in 35 fractions at 2 Gray per fraction, 5 fractions a week in two phases was delivered by linear accelerator using 3-Dimensional conformal radiotherapy technique along with concurrent chemotherapy (cisplatin 40 mg/m 2 weekly). Patients were assessed once weekly during radiation for acute toxicities with Radiation therapy oncology group (RTOG) criteria. Post treatment follow up was done monthly. Response assessment was done 3 months post RT according to World health organization (WHO) response assessment criteria. Grade ≤2 vs >2 toxicities and complete response versus partial or stable disease was correlated with PD-L1 expression in TILs using Chi square test. p value of < 0.05 was considered statistically significant. Results 51 patients were enrolled with a median age of 55.5 years (range 26-75). 90% patients had history of tobacco abuse and base of tongue was most common subsite (57%). 18/51 (35%) patients were PDL1-TIL+ve. Among these, 11(22%) were also positive for PD-L1 in tumor. Median RT dose was 70 Gray and median RT duration was 49 days. Overall grade >2 toxicity was 39.2% oral mucositis and 43% dysphagia. Radiation toxicity in terms of oral mucositis and dysphagia was more in TILs-ve patients in comparison to TIL +ve patients (table 1). At a median follow up of 10 months (range 3-18), complete response was 53% and 75% in PDL1-TIL+ve and PDL1- TIL-ve patients respectively (p=0.20).