LAUSR

64Background: Tumour immune response plays a critical role in progression and prognosis of EOC, however patterns of TILs and PD-L1 expression in primary and metastatic disease remain poorly described. Methods: Patients treated with neoadjuvant chemotherapy (NACT) for advanced EOC, between 2002-2014, and available sequential tumours (pre-NACT, post-NACT, or relapse) were retrospectively identified. Stromal TILs (sTILs) were evaluated according to the International TILs Working Group 2014 (Salgado 2015) on whole sections, and scored as a percentage of stromal area. Immune cell PD-L1 expression was evaluated by immunohistochemistry (E1L3N clone, Cell Signaling) in a smaller number of tumours. Cutoffs for analysis were: high sTILs ≥50%, PD-L1 positivity ≥5% membranous staining. Results: Among a total of 236 tumour samples from 150 patients (110 pre-NACT, 111 post-NACT, and 15 relapse tumours) median sTILs levels was significantly higher in metastatic tumours (n=151) compared with primary tumours (n=85) (media...