Claudin 18 (43-14A clone) expression in pancreatic ductal adenocarcinoma: Assessment of a potential clinical biomarker for zolbetuximab therapy

Abstract

Pancreatic ductal adenocarcinoma (PDAC) remains highly lethal, with a five-year survival rate below 15 %. Claudin 18.2 (CLDN18.2) has emerged as a novel potential therapeutic target in PDAC. Zolbetuximab, a monoclonal antibody targeting CLDN18.2, has demonstrated therapeutic benefit in gastric cancers and is now in phase 2 clinical trials for PDAC. Trial eligibility for zolbetuximab requires tumor membranous immunohistochemical staining with the pan-claudin 18 companion diagnostic antibody clone 43-14A. However, the expression of CLDN18 detected using this clone has only been evaluated in 62 patients from a single retrospective study. Herein, we report immunohistochemical staining using 43-14A on surgically resected PDAC samples (n = 120). Samples were stained following the protocol used in clinical trials, using the 43-14A VENTANA antibody in a prediluted kit, and according to the manufacturer's recommended protocol. Positive cases were defined as ≥ 75 % of tumor cells exhibiting membranous staining with an intensity of ≥ 2+. Out of 120 PDAC cases, 39 (32.5 %) stained positive for CLDN18 with 43-14A. A significant association was observed between lower tumor grade and higher 43-14A staining (p < 0.05). CLDN18-positive cases demonstrated significantly improved survival at the cohort's median overall survival (23 months, p < 0.05), suggesting that claudin expression could serve as a both a diagnostic and prognostic marker. Our findings indicate that 32.5 % of PDAC tumors in this cohort are positive for CLDN18, suggesting that a significant proportion of patients with PDAC could benefit from zolbetuximab and other CLDN18.2 targeted immunotherapies if pancreatic cancer therapeutic trials prove successful.

Keywords: 43–14a; Biomarkers; Claudin 18 protein, human; Immunohistochemistry; Pancreatic ductal carcinoma; zolbetuximab.

Graphical abstract

Fig. 1

A. Gastric mucosa with intestinal metaplasia. There is strong (3+) membranous immunopositivity for CLDN18 in normal gastric glands. Intestinal metaplasia (arrows) exhibits weak to moderate (1+ to 2+) immunopositivity for CLDN18. B. Normal pancreatic tissue, including ducts, acinar parenchyma and islets is completely negative for CLDN18.

Fig. 2

Examples of CLDN18 IHC expression intensities in PDAC samples. A. No expression (score 0) B. Predominantly score 1+ (weak intensity). C. Predominantly score 2+ (moderate intensity). D. Predominantly score 3+ (strong intensity – similar to normal gastric mucosa).

Fig. 3

Five-year overall survival for patients with PDAC positive and negative for CLDN18. Kaplan-Meier five-year overall survival curve comparing patients with CLDN18-positive tumors (n = 32) to those with CLDN18-negative tumors (n = 67) (p = 0.1244). The red dotted line indicates the entire cohort's median OS (23 months). The P-value indicates that of a fisher's exact test comparing survival between CLDN18-positive and CLDN18-negative tumors at the 23-month median OS.

Fig. 4

The distribution of 2 or 3+ intensity staining in tumors in the cohort. Most cases cluster at the left side of the distribution graph with minimal 2–3+ staining or at the right side, with at least 75 % of cells having 2–3+ staining. The red dashed line indicates the threshold for a positive result.

Fig. 5

A&B. H&E staining and corresponding CLDN18 IHC in a pancreatic adenocarcinoma negative for CLDN18 (interpreted as 0 % expression). C&D. H&E and corresponding CLDN18IHC in a PDAC interpreted as positive for claudin18 (80 % 3+ staining; 10 % 2+ staining; 5 % 1+ staining; 5 % non-staining). E&F. H&E and corresponding CLDN18 IHC in a case which fell below the threshold of 75 % 2–3+ immunopositivity for CLDN18. The stain was interpreted as 30 % 3+, 30 % 2+, 10 % 1+ and 30 % negative in this case.