Background: Diffuse gastric cancer (DGC) is the most common manifestation in germline CTNNA1 variant carriers, with one study estimating a 49–57% lifetime risk by age 80. Knowledge on CTNNA1 -associated hereditary diffuse gastric cancer (HDGC), loss-of-function mechanisms, variant-type causality, disease spectrum and cancer risks remains scarce. Objective: Explore CTNNA1 genotype–phenotype associations to improve genetic testing criteria, surveillance and risk-reduction recommendations for carriers. Design: Using molecular, clinical and population data from 1308 individuals from 351 CTNNA1- variant carrier families and 37 428 non-carriers from European and American ancestries, we analysed genotype–phenotype associations with multivariable logistic regression. With CRISPR/Cas9 CTNNA1 -knockout gastric cancer (GC) cells and CTNNA1 -humanised Drosophila , we assessed CTNNA1 -associated loss-of-function mechanisms. Results: CTNNA1 -truncating transcripts are degraded by nonsense-mediated mRNA decay (NMD), and DGCs from germline CTNNA1 -truncating carriers lose αE-catenin. These transcripts are non-functional in Drosophila , in contrast to non-truncating transcripts. DGC risk is eightfold higher in truncating, compared with non-truncating carriers. The risk of GC and lobular breast cancer (LBC) development in CTNNA1 -truncating variant carriers is fivefold and eightfold lower than in CDH1 pathogenic/likely pathogenic variant carriers, respectively. Compared with wild-type individuals, GC risk is 7-fold higher in CTNNA1 -truncating and 38-fold higher in CDH1 -truncating variant carriers. LBC is recurrent among CTNNA1 -truncating carriers, some lacking HDGC criteria. Simplification of previous criteria for CTNNA1 genetic testing produced the ‘Porto’ criteria, which increased CTNNA1 -carrier families’ pick-up rate by 9%, without performance loss compared with the HDGC 2020 clinical guidelines. Macular dystrophy patterned-2 was positively associated with non-truncating variants, specifically in the αE-catenin M-fragment. Conclusion: We provide compelling evidence supporting that CTNNA1 -truncating variants positively associate with DGC and LBC, and NMD as the pathophysiological mechanism leading to CTNNA1 downregulation. We demonstrate that compared with CDH1 , CTNNA1 is a moderate penetrance HDGC gene. This new knowledge is essential to define surveillance and/or prophylactic measures for CTNNA1 -carrier individuals and families.

De novo expressed CD44 isoforms containing exon-v6 are frequently associated with gastric cancer (GC) aggressiveness, and may predict chemotherapy response in vitro. Whether exon-v6 itself is responsible for conferring these properties to CD44v6-containing isoforms remains to be elucidated. CRISPR/Cas9 and Phosphorodiamidate Morpholino oligomers (PMOs) were used to induce specific exon-v6 skipping, maintaining the CD44 reading frame, in two GC cell lines endogenously expressing CD44v6. Cisplatin and 5-fluorouracil treatment response, and self-renewal ability was compared between CRISPR/Cas9-edited, CD44v6 knockdown and mock cells. We obtained homozygous genome-edited cell lines with exon-v6 deletion. Edited cells transcribed CD44v isoforms presenting in frame v5–v7 splicing, mimicking exon-v6 skipping. Results showed that removing specifically exon-v6 sensitizes cells to cisplatin and impairs cells’ self-renewal ability, similarly to CD44v6 knockdown. In parallel, we also tested a clinically feasible approach for transient exon-v6 skipping with a PMO-based strategy. We demonstrate that exon-v6 specific removal from CD44v isoforms increases cell sensitivity to cisplatin and impairs GC cells self-renewal. We trust that a PMO approach designed towards CD44v6 overexpressing GC cells may be a suitable approach to sensitize tumor cells for conventional therapy.

Background: Breast cancer (BC) is a major health concern and better understanding of its biology might improve treatment decisions and patient outcomes. Histone3 Lysine27 tri-methylation (H3K27me3) is a post-translational histone modification frequently associated with altered gene expression. In BC patients, lower H3K27me3 expression has been associated with worse prognosis. We assessed H3K27me3 immunoexpression with digital imaging software assistance, in a cohort of luminal-like BC patients with long-term follow-up time and evaluated its association with clinically relevant endpoints and its clinical usefulness. Methods: H3K27me3 immunoexpression was assessed, by means of digital-imaging system, in archival tissue samples of 160 luminal A/B-like HER2-negative invasive BC, stages I-III. Survival analysis was performed using Kaplan-Meier and Cox regression. Cases were categorized as ‘low’ or ‘high’ expression based on cut-off defined by receiver operating characteristic (ROC) curve analysis. Results: The patient cohort showed a median age of 61-years, with a median follow-up time of 11.7 years. Low H3K27me3 expression (below 85% cut-off) was significantly associated with recurrence, both in univariable (HR = 1.99, 95%CI 1.066–3.724) and multivariable analysis when adjusting for grade and age (HR = 1.89, 95%CI 1.004–3.559). A trend for higher risk of death in low H3K27me3 expression BC was observed (p = 0.069), reaching statistical significance in younger patients (p = 0.021). Conclusions: H3K27me3 immunoexpression assessed by digital imaging scoring software is an independent prognosis biomarker in luminal-like BC patients and may assist in more individualized adjuvant treatment decisions, thus potentially reducing recurrences after curative-intent treatment, while sparing unnecessary toxicity.

CRISPR/Cas9-mediated homology-directed repair (HDR) allows precise gene editing, but its efficiency remains low for certain cell types, such as human induced pluripotent stem cells (hiPSCs). In this study, we aimed to introduce the CTNNA1: c.2023C>T (p.Q675*) genetic alteration, which is associated with Hereditary Diffuse Gastric Cancer, into hiPSCs using CRISPR/Cas9. We designed a single-guide RNA targeting the alteration site and a single-stranded oligonucleotide donor DNA template for HDR-based repair. Herein, we report the successful introduction of the CTNNA1: c.2023C>T homozygous alteration in one hiPSC line, which resulted in severe phenotypic changes, including impaired colony formation and cell proliferation. Additionally, we established a straightforward protocol to assess hiPSCs karyotype integrity, ensuring the chromosomal stability required for the gene-editing process. This protocol involves routine G-banding analysis that is required for regular quality controls during handling of hiPSCs. This study demonstrates an efficient approach to precisely edit hiPSCs by CRISPR/Cas9 and highlights the essential role of CTNNA1 expression in maintaining hiPSC viability. Our methodology provides a valuable framework for modeling disease-associated alterations in human-derived cellular models that can be reproduced for other genes and other types of cell lines.