Abstract 451P
Background
Programmed death-ligand 1 (PD-L1) expression determines eligibility for immunotherapy treatment (tx) in patients (pts) with advanced EGC. However, limited data exists on concordance rate between PD-L1 combined positive score (CPS) in diagnostic biopsies and matched surgical specimens and the effects of neoadjuvant (N-ADJ) tx on the expression of PD-L1 remain unclear. Our study aims to evaluate the reliability of PD-L1 expression on diagnostic biopsies compared with matched surgical specimens.
Methods
This is a retrospective, monocentric, observational study including pts with resectable EGC (cTNM II-IVa) treated at Istituto Oncologico Veneto-IRCCS. Tissue microarray sections from diagnostic biopsies and resected specimens were evaluated by immunohistochemistry. PD-L1 CPS was defined as negative (< 1), low (1-4), intermediate (5-9) or high (≥10).
Results
From May 2014 to December 2023 a total of 179 pts having both biopsy and surgical specimen at our Institution (median age 62 year [range 32–89], male: 70%, ECOG PS 0: 58%, adenocarcinoma histology: 92%, gastric and GEJ location: 86%), underwent surgery upfront (n=75, 42%) or were treated with chemotherapy (n=76,42.4%) or concomitant chemoradiotherapy (n=28,15.6%). In the whole population, the distribution of PD-L1 expression in biopsy and surgical specimens was similar: negative (n=13 vs. n=12), low (n=43 vs. n=47), intermediate (n=30 vs. n=32), and high (n=93 vs. n=88). However, matching biopsy and surgical samples the PD-L1 concordance rate was only 49.7%. In samples coming from pts treated with upfront surgery, the concordance rate between the two specimens was 56%, while in pts receiving N-ADJ tx was 45.2%. In pts undergoing N-ADJ tx, PD-L1 expression in surgical samples increased in 24 cases (23.1%), decreased in 33 cases (31.7%), and remained unchanged in 47 cases (45.2%). N-ADJ tx significantly altered PD-L1 expression (OR 1.82, p=0.05).
Conclusions
In our study, PD-L1 expression exhibits temporal heterogeneity between primary biopsies and surgical specimens in EGC, significantly increased in pts receiving N-ADJ tx. This heterogeneity should be taken into account when choosing treatment in a metastatic setting.
Legal entity responsible for the study
The authors.
Funding
Has not received any funding.
Disclosure
F. Bergamo: Financial Interests, Invited Speaker: Eli Lilly, MSD, Eisai, Bayer; Financial Interests, Advisory Board: Novartis, Servier. S. Lonardi: Financial Interests, Personal, Advisory Board: Amgen, Merck Serono, Lilly, Servier, AstraZeneca, MSD, Incyte, Daiichi Sankyo, Bristol Myers Squibb, Astellas, GSK, Takeda, Bayer; Financial Interests, Personal, Invited Speaker: Pierre Fabre, GSK, Roche, Servier, Amgen, Bristol Myers Squibb, Incyte, Lilly, Merck Serono, MSD; Financial Interests, Institutional, Invited Speaker: Amgen, Merck Serono, Bayer, Roche, Lilly, AstraZeneca, Bristol Myers Squibb; Non-Financial Interests, Member of Board of Directors, Italian No-Profit Oncology Research Foundation supporting academic Clinical trials: GONO Foundation. M. Fassan: Financial Interests, Advisory Board: Astellas Pharma, Pierre Fabre, MSD, AstraZeneca, Janssen, GSK, BMS, Incyte, Amgen, Novartis, Roche. All other authors have declared no conflicts of interest.