Targeted genotyping for recurring variants in cancer susceptibility genes in non-Ashkenazi Jewish patients with breast cancer diagnosed ≥50 years.

PURPOSE: Several recurring pathogenic variants (PVs) in BRCA1/BRCA2 and additional cancer susceptibility genes are described in the ethnically diverse Israeli population. Since 2019, testing for these recurring PVs is reimbursed unselectively for all patients with breast cancer (BC) in Israel. The aim was to evaluate the yield of genotyping for these PVs in non-Ashkenazi Jewish (AJ) patients with BC diagnosed ≥age 50 years. METHODS: Clinical and genotyping data of all patients with BC undergoing oncogenetic counseling at the Oncology Institute at Sheba Medical Center from June 2017 to December 2023 were reviewed. RESULTS: Of 2706 patients with BC (mean age at diagnosis, 54 years; range, 20-92 years) counseled, 515 patients of non-AJ (all four grandparents) descent, diagnosed ≥age 50 years of age were genotyped, 55 with triple-negative BC (TNBC) and 460 with non-TNBC. One of the recurring PVs in BRCA1/BRCA2 were detected in 12.7% (7/55) of TNBC patients and 0.65% (3/460) of non-TNBC. One patient with non-TNBC had PMS2 PV. Low-penetrance variants were found in 2.5% of genotyped TNBC and in 3.7% of patients with non-TNBC, including CHEK2 c.499G>A (n = 3), APC c.3920T > A (n = 4), and heterozygous MUTYH c.1187G>A (n = 5). Following first-pass genotyping, 146 patients performed multigene panel testing, none carried a BRCA1/BRCA2 PV, and only 5/127 non-TNBC (3.9%) harbored PVs in CHEK2 (n = 2, c.846+1G>C and c.592+3A>T), ATM c.103C>T (n = 2), and NBN c.966C>G (n = 1). CONCLUSIONS: The observed low rates of PV detection in non-AJ non-TNBC cases ≥age 50 years at diagnosis, mostly for clinically insignificant variants, questions the justification of unselected genotyping in this subset of patients.

Double heterozygosity for TP53 and BRCA1 mutations: clinical implications in populations with founder mutations.

PURPOSE: The co-occurrence or double heterozygosity of pathogenic/likely pathogenic sequence variants (P/LPSVs) in major cancer susceptibility genes has rarely been reported. Such co-occurrence raises the issues of accurate genetic counseling, preferred recommended surveillance scheme, and the use of preimplantation genetic diagnosis (PGD). METHODS: A clinical report of an Ashkenazi Jewish (AJ) family with co occurrence of two PSVs in BRCA1 and TP53 and a literature search. RESULTS: In an AJ family with a substantial history of cancer limited to the maternal side, two siblings co-harbored TP53 (c.733C>A; p.G245S) and the predominant 5266dup BRCA1 mutation, originating from the mother and the father, respectively. PGD is ongoing. Four families were thus far reported as double heterozygotes for both BRCA1/BRCA2 and TP53. Based on the limited available data, it seems that the phenotype in double PSV heterozygotes is not more severe than in single PSV carrier in either gene. CONCLUSIONS: This family highlights the need to genotype both parents, especially in populations with founder mutations, when a BRCA1 mutation is detected in an offspring, regardless of family history. The combination of mutations in these two genes presents a challenge for PGD since both genes are located on chromosome 17.

Multigene panel testing in unselected Israeli breast cancer cases: mutational spectrum and use of BRCA1/2 mutation prediction algorithms.

BACKGROUND: Studies assessing the contribution of non-BRCA1/2 gene mutations to inherited breast cancer (BC) predisposition consistently reported low (up to 4%) yield. The current study aimed at assessing the spectrum of non-BRCA mutations in unselected Israeli BC cases and the utility of BRCAPRO and Penn II models, as tools for prediction of detecting non-BRCA1/2 mutations in Israeli BC patients who tested negative for the predominant Jewish BRCA1/2 mutations. METHODS: All consecutive Jewish Israeli BC patients at the Sheba Medical center who tested negative for the predominant BRCA1/2 mutations and elected to perform multigene panel testing were included. For each patient probability of BRCA mutation detection was calculated by the Penn II algorithm and the BRCAPRO tool. RESULTS: Overall, 144 cases were included (median age at diagnosis was 48, range 20-73 years); 48% were Ashkenazim. One patient harbored a non-founder BRCA1 mutation (c.5434C>G; p.P1812A). Pathogenic/likely pathogenic (P/LP) mutations in non-BRCA1/2 genes were detected in additional 14/144 patients, including CHEK2 (n = 5), RAD51D (n = 2), MSH6 (n = 2), and one each in ATM, RET, TP53, NBN, and BAP1. Using a cutoff of 15% probability of BRCA mutation detection, both models accurately predicted the observed carrier rate of non-BRCA mutations. CONCLUSIONS: In unselected Jewish Israeli BC patients, the rate of detecting non-founder BRCA1/2 mutations is low, with CHEK2 mutations detected in 3.4% of cases. BRCA1/2 mutation prediction models may be utilized for selecting patients eligible for further multigene panel testing after exclusion of predominant BRCA1/2 mutations.

The Diagnostic Yield and Implications of Targeted Founder Pathogenic Variant Testing in an Israeli Cohort.

Founder pathogenic variants (PVs) are prevalent in Israel. This study investigated the current practice of offering cancer patients two-step genetic testing, starting with targeted testing for recurring founder PVs, followed, if negative, by next-generation sequencing. A total of 2128 subjects with cancer or a positive family history underwent oncogenetic testing with a panel of 51 recurring PVs at a tertiary medical center in March 2020-January 2023. Those with a known familial PV (n = 370) were excluded from the analysis. Among the remainder, 128/1758 (7%) were heterozygous for at least one variant, and 44 (34%) carried a PV of medium-high penetrance (MHPV). Cancer was diagnosed in 1519/1758 patients (86%). The diagnostic yield of founder MHPV testing was 2% in cancer patients and 4% in healthy individuals with a positive family history. It was higher in Ashkenazi Jews than non-Ashkenazi Jews and Arabs, but not over 10% for any type of cancer, and it was significantly higher in younger (<40 years) than older (>50 years) individuals (7% vs. 1%). Eighty-four of the heterozygotes (66%), mostly Ashkenazi Jews, harbored a low-penetrance variant (LPV) not associated with the diagnosed cancer, usually APC c.3902T>A. These findings question the advantage of two-step testing. LPVs should not be included in targeted testing because this can lead to an overestimation of the yield, and their detection does not preclude further comprehensive testing.