Genotype-first approach to identify associations between CDH1 germline variants and cancer phenotypes: a multicentre study by the European Reference Network on Genetic Tumour Risk Syndromes.

BACKGROUND: Truncating pathogenic or likely pathogenic variants of CDH1 cause hereditary diffuse gastric cancer (HDGC), a tumour risk syndrome that predisposes carrier individuals to diffuse gastric and lobular breast cancer. Rare CDH1 missense variants are often classified as variants of unknown significance. We conducted a genotype-phenotype analysis in families carrying rare CDH1 variants, comparing cancer spectrum in carriers of pathogenic or likely pathogenic variants (PV/LPV; analysed jointly) or missense variants of unknown significance, assessing the frequency of families with lobular breast cancer among PV/LPV carrier families, and testing the performance of lobular breast cancer-expanded criteria for CDH1 testing. METHODS: This genotype-first study used retrospective diagnostic and clinical data from 854 carriers of 398 rare CDH1 variants and 1021 relatives, irrespective of HDGC clinical criteria, from 29 institutions in ten member-countries of the European Reference Network on Tumour Risk Syndromes (ERN GENTURIS). Data were collected from Oct 1, 2018, to Sept 20, 2022. Variants were classified by molecular type and clinical actionability with the American College of Medical Genetics and Association for Molecular Pathology CDH1 guidelines (version 2). Families were categorised by whether they fulfilled the 2015 and 2020 HDGC clinical criteria. Genotype-phenotype associations were analysed by Student's t test, Kruskal-Wallis, χ2, and multivariable logistic regression models. Performance of HDGC clinical criteria sets were assessed with an equivalence test and Youden index, and the areas under the receiver operating characteristic curves were compared by Z test. FINDINGS: From 1971 phenotypes (contributed by 854 probands and 1021 relatives aged 1-93 years), 460 had gastric and breast cancer histology available. CDH1 truncating PV/LPVs occurred in 176 (21%) of 854 families and missense variants of unknown significance in 169 (20%) families. Multivariable logistic regression comparing phenotypes occurring in families carrying PV/LPVs or missense variants of unknown significance showed that lobular breast cancer had the greatest positive association with the presence of PV/LPVs (odds ratio 12·39 [95% CI 2·66-57·74], p=0·0014), followed by diffuse gastric cancer (8·00 [2·18-29·39], p=0·0017) and gastric cancer (7·81 [2·03-29·96], p=0·0027). 136 (77%) of 176 families carrying PV/LPVs fulfilled the 2015 HDGC criteria. Of the remaining 40 (23%) families, who did not fulfil the 2015 criteria, 11 fulfilled the 2020 HDGC criteria, and 18 had lobular breast cancer only or lobular breast cancer and gastric cancer, but did not meet the 2020 criteria. No specific CDH1 variant was found to predispose individuals specifically to lobular breast cancer, although 12 (7%) of 176 PV/LPV carrier families had lobular breast cancer only. Addition of three new lobular breast cancer-centred criteria improved testing sensitivity while retaining high specificity. The probability of finding CDH1 PV/LPVs in patients fulfilling the lobular breast cancer-expanded criteria, compared with the 2020 criteria, increased significantly (AUC 0·92 vs 0·88; Z score 3·54; p=0·0004). INTERPRETATION: CDH1 PV/LPVs were positively associated with HDGC-related phenotypes (lobular breast cancer, diffuse gastric cancer, and gastric cancer), and no evidence for a positive association with these phenotypes was found for CDH1 missense variants of unknown significance. CDH1 PV/LPVs occurred often in families with lobular breast cancer who did not fulfil the 2020 HDGC criteria, supporting the expansion of lobular breast cancer-centred criteria. FUNDING: European Reference Network on Genetic Tumour Risk Syndromes, European Regional Development Fund, Fundação para a Ciência e a Tecnologia (Portugal), Cancer Research UK, and European Union's Horizon 2020 research and innovation programme.

Phenotypic heterogeneity of hereditary diffuse gastric cancer: report of a family with early-onset disease.

BACKGROUND AND AIMS: The time course for the development of clinically significant hereditary diffuse gastric cancer (HDGC) is unpredictable. Little is known about the progression from preclinical, indolent lesions to widely invasive, aggressive phenotypes. Gastroendoscopy often fails to detect early lesions, and risk-reducing/prophylactic total gastrectomy (PTG) is the only curative approach. We present an HDGC family with early-onset disease in which clinical and histologic findings provided insight into the understanding of different HDGC phenotypes. METHODS: The proband was diagnosed at age 18 years with widely invasive, metastatic DGC. CDH1 genetic testing identified a pathogenic, germline CDH1 variant (c.1901C>T, p.Ala634Val). Thirty family members were tested, and 15 CDH1 carriers were identified. RESULTS: Six family members had PTG, with negative preoperative workup. The proband's 14-year-old sister is the youngest patient, reported to date, to have PTG after negative preoperative biopsy sampling. Intramucosal HDGC foci were detected in all PTG specimens (1-33). In contrast to the "indolent" phenotype of these foci, the aggressive DGC from the proband showed pleomorphic cells, absent E-cadherin expression, increased proliferation (Ki-67 index), and activation of oncogenic events (p53, pSrc and pStat3 overexpression). All family members had Helicobacter pylori gastritis. Cag-A-positive strains were detected in all specimens, except in the proband's sister. CONCLUSIONS: HDGC is a heterogeneous disease regarding clinical behavior, endoscopic findings, histopathologic features, and immunophenotypic/molecular profile. The presence of bizarre, pleomorphic cells in endoscopic biopsy specimens is suggestive of advanced disease and should prompt clinical intervention. The involvement of a full multidisciplinary team is essential for the management of these patients.

Differences among a Portuguese cohort of BRCA pathogenic/likely pathogenic variants carriers choosing risk-reducing mastectomy or intensive breast surveillance.

PURPOSE: Women with BRCA1 and BRCA2 (BRCA1/2) pathogenic/likely pathogenic (P/LP) variants have a higher risk to develop breast and ovarian cancer. In structured high-risk clinics, risk-reducing measures are adopted. This study aimed at characterizing these women and identify factors that may have influenced their choice between risk reduction mastectomy (RRM) and intensive breast surveillance (IBS). METHODS: This study reviewed retrospectively 187 clinical records of affected and unaffected women with P/LP variants of the BRCA1/2 genes, from 2007 to 2022, of which 50 chose RRM, while 137 chose IBS. The research focused on personal and family history and tumor characteristics and their relation with the preventive option chosen. RESULTS: Among women with personal history of breast cancer, a higher proportion opted for RRM compared to those asymptomatic (34.2% vs 21.3%, p = 0.049), with younger age determining the option for RRM (38.5 years vs 44.0 years, p < 0.001). Among women with personal history of ovarian cancer, a higher proportion opted for RRM compared to those without that history (62.5% vs 25.1%, p = 0.033), with younger age determining the option for RRM (42.6 years vs 62.7 years, p = 0.009). Women who had bilateral salpingo-oophorectomy were more likely to choose RRM than those who did not (37.3% vs 18.3%, p = 0.003). Family history was not associated with preventive option (33.3% vs 25.3, p = 0.346). CONCLUSIONS: The decision for the preventive option is multifactorial. In our study, personal history of breast or ovarian cancer, younger age at diagnosis, and previous bilateral salpingo-oophorectomy were associated with the choice of RRM. Family history was not associated with the preventive option.

A comprehensive study on surveillance outcomes of a male population followed at a hereditary breast cancer high-risk consultation at a Portuguese tertiary hospital.

INTRODUCTION: Men born with pathogenic/likely pathogenic variants in genes associated with the Hereditary Breast and Ovarian Cancer Syndrome have a higher risk to develop breast cancer and other cancers (such as prostate cancer) and should undergo adequate surveillance protocols in highly specialized Centers. METHODS: A retrospective study was conducted to assess these genetic variants' epidemiological and phenotypical manifestations in male carriers, as well as the efficacy of the surveillance protocol and compliance toward it through a survey. During follow-up, a genetic panel for testing was implemented, the starting age for surveillance was delayed, and the six-month screening interval was extended to annual. RESULTS: A total of 104 men from a tertiary hospital's High-Risk Consultation were included, 102 with positive genetic testing for BRCA1 (n = 31), BRCA2 (n = 55), both BRCA2 and another gene (n = 5), CDH1 (n = 2), CHEK2 (n = 4), NF1 (n = 1), RAD51C (n = 4), and an additional two men with no actionable genetic variant identified. The follow-up period ranged from 1 to 13 years, and only one man developed cancer. Survey responses from 48 men in active surveillance showed that more than half recognizes their carrier status and consequent surveillance impact on their life, including the risk of transmission to offspring, fear of future cancer, meaningful distress, and feeling of injustice. Biannual surveillance was not actively detecting more cancer disease cases, confirming the adequacy of the currently implemented protocol CONCLUSION: With support of Genetics to fulfill the current gaps in high-risk management, the proposed redefinition of surveillance protocol would adapt it to the population needs and concerns.

The CDH1 c.1901C>T Variant: A Founder Variant in the Portuguese Population with Severe Impact in mRNA Splicing.

Hereditary diffuse gastric cancer (HDGC) caused by CDH1 variants predisposes to early-onset diffuse gastric (DGC) and lobular breast cancer (LBC). In Northern Portugal, the unusually high number of HDGC cases in unrelated families carrying the c.1901C>T variant (formerly known as p.A634V) suggested this as a CDH1-founder variant. We aimed to demonstrate that c.1901C>T is a bona fide truncating variant inducing cryptic splicing, to calculate the timing of a potential founder effect, and to characterize tumour spectrum and age of onset in carrying families. The impact in splicing was proven by using carriers' RNA for PCR-cloning sequencing and allelic expression imbalance analysis with SNaPshot. Carriers and noncarriers were haplotyped for 12 polymorphic markers, and the decay of haplotype sharing (DHS) method was used to estimate the time to the most common ancestor of c.1901C>T. Clinical information from 58 carriers was collected and analysed. We validated the cryptic splice site within CDH1-exon 12, which was preferred over the canonical one in 100% of sequenced clones. Cryptic splicing induced an out-of-frame 37bp deletion in exon 12, premature truncation (p.Ala634ProfsTer7), and consequently RNA mediated decay. The haplotypes carrying the c.1901C>T variant were found to share a common ancestral estimated at 490 years (95% Confidence Interval 445-10,900). Among 58 carriers (27 males (M)-31 females (F); 13-83 years), DGC occurred in 11 (18.9%; 4M-7F; average age 33 ± 12) and LBC in 6 females (19.4%; average age 50 ± 8). Herein, we demonstrated that the c.1901C>T variant is a loss-of-function splice-site variant that underlies the first CDH1-founder effect in Portugal. Knowledge on this founder effect will drive genetic testing of this specific variant in HDGC families in this geographical region and allow intrafamilial penetrance analysis and better estimation of variant-associated tumour risks, disease age of onset, and spectrum.