The impact of claudin-18.2 expression in patients with advanced gastric cancer treated with nivolumab.

439 Background: Claudin-18.2 (CLDN 18.2) is the components of tight junction and one of the therapeutic targets in advanced gastric cancer (AGC). It has been reported that the tumor microenvironment in CLDN18.2 high AGC contains more PD-1 negative CD8+ T cells than in CLDN18.2 low, which may make anti-PD-1 antibodies less effective. However, the data on the association between CLDN18.2 expression and prognosis in patients with AGC treated with nivolumab (NIVO) is limited. Methods: Patients who received NIVO monotherapy as third- or later-line treatment (NIVO group) and those who received only fluoropyrimidine, platinum and taxanes (non-NIVO group) at our hospital between 2015 and 2019 were enrolled. High CLDN18.2 expression was defined as ≥40% positive tumor cells with moderate to strong membranous staining on immunohistochemistry. Overall survival (OS) and progression-free survival (PFS) were compared according to CLDN18.2 expression and combined positivity score (CPS). Results: There were 71 and 50 patients in the NIVO and non-NIVO groups, respectively. Patient characteristics at first-line chemotherapy in the NIVO/non-NIVO groups were median age 67 (range, 34-83)/64.5 (29-80) years; performance status 0, 22 (31%)/23 (46%); peritoneal metastasis 38 (54%)/26 (52%); liver metastasis 15 (21%)/6 (12%); CLDN18.2 high 31 (44%)/25 (50%). In the NIVO group, patient characteristics did not differ between CLDN18.2 high and low except for peritoneal metastasis (25 [81%]/22 [55%]). Nine patients (29%) were CLDN18.2 high with CPS≥1, and 14 (35%) were CLDN18.2 low with CPS≥1. OS from first-line chemotherapy did not differ between CLDN18.2 high and low in the non-NIVO group (median, 18.4 months [95%CI, 10.7-32.4] vs. 16.9 months [95%CI, 14.8-21.4], HR 0.94 [95%CI, 0.50-1.78], p=0.847). In the NIVO group, OS from first-line chemotherapy and OS and PFS after starting NIVO did not differ between CLDN18.2 high and low; however, patients with CLDN18.2 high and CPS≥1 had longer OS after starting NIVO (median, 14.8 months [95%CI, 4.2-NR] vs. 3.6 months [95%CI, 2.0-6.9], HR 0.27 [95%CI, 0.11-0.68], p=0.012) and PFS after starting NIVO (median, 3.5 months [95%CI, 0.7-NR] vs. 1.7 months [95%CI, 1.1-3.1], HR 0.38 [95%CI, 0.15-0.97], p=0.033) than those with CLDN 18.2 high and CPS<1. Patients with CLDN18.2 high and CPS≥1 had a trend of longer OS from first-line chemotherapy than those with CLDN 18.2 high and CPS<1 (median, 37.4 months [95%CI, 11.1-NR] vs. 14.8 months [95%CI, 9.4-31.2], HR 0.47 [95%CI, 0.17-1.31], p=0.12). In the CLDN18.2 low group, OS and PFS did not differ between CPS≥1 and <1. Conclusions: With CLDN18.2 high, CPS≥1 was associated with longer survival in AGC treated with NIVO.