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.

Background/Objectives: One study of pancreatic ductal adenocarcinoma has found expression of glypican-3 (GPC3) and cytokeratin-19 (CK19) determined by immunohistochemistry to be associated with higher stage and grade disease, with a more adverse prognosis. The reported 44% rate of GPC3 expression in pancreatic cancer raises the important possibility that targeted immunotherapies currently in development for hepatocellular carcinoma may also prove useful for GPC3-expressing pancreatic cancers. The present study aims to determine if a similar expression pattern of these markers and stage/grade/prognostic associations is present in our Canadian patient population. Methods: Patients with a pancreatic surgical resection for adenocarcinoma or neuroendocrine tumor (NET) were identified from pathology records over a 5-year period. Immunohistochemistry for GPC3 and CK19 was performed on archived tumor tissue and the proportion of positive cells and intensity of staining were recorded. Grade, stage, and overall survival were compared in patients with NETs that were CK19-positive versus -negative. Results: All 72 pancreatic adenocarcinomas and 20 NETs tested were negative for GPC3, apart from a single case of pancreatic adenocarcinoma. All 72 adenocarcinomas were positive for CK19 expression. Half of the NETs were positive for CK19. There was no correlation between CK19 expression in NETs and tumor grade, lymph node metastasis, distant metastasis, or overall survival. Conclusions: We are skeptical of the reported prognostic value of GPC3 and CK19 in pancreatic adenocarcinomas. CK19 as a prognostic marker in NETs has potential for further study. The results with our protocol for GPC3 immunohistochemistry suggest that pancreatic cancer may be a less promising target for GPC3-targeted immunotherapies than previously thought.

Background: Pancreatic ductal adenocarcinoma (PDAC) remains one of the deadliest cancers, and has limited options for treatment. Low immune infiltration, desmoplastic stroma, and poor tumour immunogenicity are all expected to contribute to PDAC’s rapid progression and limited response to existing immunotherapies. PDAC tumours are mosaics of different sub-tumour microenvironments, including some that do contain immune cells. We hypothesized that increasing frequency of lymphocyte:tumour interactions would correlate with lengthened survival for patients with PDAC. Methods: Using multiplex immunofluorescence, digital pathology, and computational analyses, we profiled the spatial distribution, co-localization, and neighbourhood architecture of immune cells in tumours from 73 patients with PDAC. Results: Higher densities of CD3+CD8– (CD4+) T cells were associated with improved five-year overall survival, particularly when enriched at the tumour-stroma boundary (i.e. peritumoural). CD3+CD8-T cells, CD8+ T cells (CD3+CD8+), and B cells (CD20+) frequently co-infiltrated and co-localized, forming distinct immune neighbourhoods indicative of organized adaptive immunity. We defined three common immune neighbourhoods within PDAC (1) Macrophage-dominant; (2) T cell dominant; and (3) Disorganized. With greater tumour and peri-tumoural area represented by the T cell dominant neighbourhood, overall survival was increased. The other neighbourhoods were not significantly associated with outcomes. Conclusion: Immune cells self-assemble in predictable patterns in PDAC. The presence of T cell dominant neighbourhoods, which we interpret as supporting ongoing immune activation, best predict lengthened survival. Spatially organized immune interactions may serve as prognostic indicators and inform future studies for immunotherapies in PDAC.