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Tumor sequencing is useful to refine the analysis of germline variants in unexplained high-risk breast cancer families.

ABSTRACT: BACKGROUND:Multigene panels are routinely used to assess for predisposing germline mutations in families at high breast cancer risk. The number of variants of unknown significance thereby identified increases with the number of sequenced genes. We aimed to determine whether tumor sequencing can help refine the analysis of germline variants based on second somatic genetic events in the same gene. METHODS:Whole-exome sequencing (WES) was performed on whole blood DNA from 70 unrelated breast cancer patients referred for genetic testing and without a BRCA1, BRCA2, TP53, or CHEK2 mutation. Rare variants were retained in a list of 735 genes. WES was performed on matched tumor DNA to identify somatic second hits (copy number alterations (CNAs) or mutations) in the same genes. Distinct methods (among which immunohistochemistry, mutational signatures, homologous recombination deficiency, and tumor mutation burden analyses) were used to further study the role of the variants in tumor development, as appropriate. RESULTS:Sixty-eight patients (97%) carried at least one germline variant (4.7?±?2.0 variants per patient). Of the 329 variants, 55 (17%) presented a second hit in paired tumor tissue. Of these, 53 were CNAs, resulting in tumor enrichment (28 variants) or depletion (25 variants) of the germline variant. Eleven patients received variant disclosure, with clinical measures for five of them. Seven variants in breast cancer-predisposing genes were considered not implicated in oncogenesis. One patient presented significant tumor enrichment of a germline variant in the oncogene ERBB2, in vitro expression of which caused downstream signaling pathway activation. CONCLUSION:Tumor sequencing is a powerful approach to refine variant interpretation in cancer-predisposing genes in high-risk breast cancer patients. In this series, the strategy provided clinically relevant information for 11 out of 70 patients (16%), adapted to the considered gene and the familial clinical phenotype.

SUBMITTER: Van Marcke C

PROVIDER: S-EPMC7161277 | biostudies-literature | 2020 Apr

REPOSITORIES: biostudies-literature

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Tumor sequencing is useful to refine the analysis of germline variants in unexplained high-risk breast cancer families.

Van Marcke Cédric C Helaers Raphaël R De Leener Anne A Merhi Ahmad A Schoonjans Céline A CA Ambroise Jérôme J Galant Christine C Delrée Paul P Rothé Françoise F Bar Isabelle I Khoury Elsa E Brouillard Pascal P Canon Jean-Luc JL Vuylsteke Peter P Machiels Jean-Pascal JP Berlière Martine M Limaye Nisha N Vikkula Miikka M Duhoux François P FP

Breast cancer research : BCR 20200415 1

<h4>Background</h4>Multigene panels are routinely used to assess for predisposing germline mutations in families at high breast cancer risk. The number of variants of unknown significance thereby identified increases with the number of sequenced genes. We aimed to determine whether tumor sequencing can help refine the analysis of germline variants based on second somatic genetic events in the same gene.<h4>Methods</h4>Whole-exome sequencing (WES) was performed on whole blood DNA from 70 unrelate ...[more]

PMID: 32295625

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Project description:ImportanceTumor genetic sequencing identifies potentially targetable genetic alterations with therapeutic implications. Analysis has concentrated on detecting tumor-specific variants, but recognition of germline variants may prove valuable as well.ObjectiveTo estimate the burden of germline variants identified through routine clinical tumor sequencing.Design, setting, and participantsPatients with advanced cancer diagnoses eligible for studies of targeted agents at Memorial Sloan Kettering Cancer Center are offered tumor-normal sequencing with MSK-IMPACT, a 341-gene panel. We surveyed the germline variants seen in 187 overlapping genes with Mendelian disease associations in 1566 patients who had undergone tumor profiling between March and October 2014.Main outcomes and measuresThe number of presumed pathogenic germline variants (PPGVs) and variants of uncertain significance per person in 187 genes associated with single-gene disorders and the proportions of individuals with PPGVs in clinically relevant gene subsets, in genes consistent with known tumor phenotypes, and in genes with evidence of second somatic hits in their tumors.ResultsThe mean age of the 1566 patients was 58 years, and 54% were women. Presumed pathogenic germline variants in known Mendelian disease-associated genes were identified in 246 of 1566 patients (15.7%; 95% CI, 14.0%-17.6%), including 198 individuals with mutations in genes associated with cancer susceptibility. Germline findings in cancer susceptibility genes were concordant with the individual's cancer type in only 81 of 198 cases (40.9%; 95% CI, 34.3%-47.9%). In individuals with PPGVs retained in the tumor, somatic alteration of the other allele was seen in 39 of 182 cases (21.4%; 95% CI, 16.1%-28.0%), of which 13 cases did not show a known correlation of the germline mutation and a known syndrome. Mutations in non-cancer-related Mendelian disease genes were seen in 55 of 1566 cases (3.5%; 95% CI, 27.1%-45.4%). Almost every individual had more than 1 variant of uncertain significance (1565 of 1566 patients; 99.9%; 95% CI, 99.6%-99.9%).Conclusions and relevanceGermline variants are common in individuals undergoing tumor-normal sequencing and may reveal otherwise unsuspected syndromic associations.

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Tumor sequencing is useful to refine the analysis of germline variants in unexplained high-risk breast cancer families.

Publications

Tumor sequencing is useful to refine the analysis of germline variants in unexplained high-risk breast cancer families.

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