Concurrent pathogenic variations in patients with hereditary cancer syndromes

Secondary findings in genes related to cancer phenotypes in Turkish exome sequencing data from 2020 individuals

Big data generated from exome sequencing (ES) and genome sequencing (GS) analyses can be used to detect actionable and high-penetrance variants that are not directly associated with the primary diagnosis of patients but can guide their clinical follow-up and treatment. Variants that are classified as pathogenic/likely pathogenic and are clinically significant but not directly associated with the primary diagnosis of patients are defined as secondary findings (SF). The aim of this study was to examine the frequency and variant spectrum of cancer-related SF in 2020 Turkish ES data and to discuss the importance of the presence of cancer-related SF in at-risk family members in terms of genetic counseling and follow-up. A total of 2020 patients from 2020 different families were evaluated by ES. SF were detected in 28 unrelated cases (1.38%), and variants in BRCA2 (11 patients) and MLH1 (4 patients) genes were observed most frequently. A total of 21 different variants were identified, with 4 of them (c.9919_9932del and c.3653del in the BRCA2 gene, c.2002A>G in the MSH2 gene, c.26_29del in the TMEM127 gene) being novel variations. In three different families, c.1189C>T (p.Gln397*) variation in BRCA2 gene was detected, suggesting that this may be a common variant in the Turkish population. This study represents the largest cohort conducted in the Turkish population, examining the frequency and variant spectrum of cancer-related SF. With the identification of frequent variations and the detection of novel variations, the findings of this study have contributed to the variant spectrum. Genetic testing conducted in family members is presented as real-life data, showcasing the implications in terms of counseling, monitoring, and treatment through case examples.

Double Heterozygous Pathogenic Variants in TP53 and CHEK2 in Boy with Undifferentiated Embryonal Sarcoma of the Liver

Undifferentiated embryonal sarcoma of the liver is a rare mesenchymal malignancy that predominantly occurs in children. The relationship between this tumor entity and germline pathogenic variants (PVs) remains undefined. Here, we present the clinical case of a male patient diagnosed with undifferentiated embryonal sarcoma of the liver. Both germline and tumor samples were analyzed using next-generation sequencing. In the tumor tissue, PVs in TP53 (NM_000546.5):c.532del p.(His178Thrfs*69) and CHEK2 (NM_007194.4):c.85C>T p.(Gln29*) were identified, with both confirmed to be of germline origin. Copy number analyses indicated a loss of the wildtype TP53 allele in the tumor, consistent with a second hit, while it was the variant CHEK2 allele that was lost in the tumor. Our data indicate that the germline TP53 PV acts as a driver of tumorigenesis in the reported case and support a complex interaction between the germline TP53 and CHEK2 PVs. This case highlights the dynamic interplays of genetic alterations in tumorigenesis and emphasizes the need for continued investigation into the complex interactions between TP53 and CHEK2 PVs and into the association of undifferentiated embryonal sarcoma of the liver and Li-Fraumeni syndrome.

Co-observation of germline pathogenic variants in breast cancer predisposition genes: Results from analysis of the BRIDGES sequencing dataset

Co-observation of a gene variant with a pathogenic variant in another gene that explains the disease presentation has been designated as evidence against pathogenicity for commonly used variant classification guidelines. Multiple variant curation expert panels have specified, from consensus opinion, that this evidence type is not applicable for the classification of breast cancer predisposition gene variants. Statistical analysis of sequence data for 55,815 individuals diagnosed with breast cancer from the BRIDGES sequencing project was undertaken to formally assess the utility of co-observation data for germline variant classification. Our analysis included expected loss-of-function variants in 11 breast cancer predisposition genes and pathogenic missense variants in BRCA1, BRCA2, and TP53. We assessed whether co-observation of pathogenic variants in two different genes occurred more or less often than expected under the assumption of independence. Co-observation of pathogenic variants in each of BRCA1, BRCA2, and PALB2 with the remaining genes was less frequent than expected. This evidence for depletion remained after adjustment for age at diagnosis, study design (familial versus population-based), and country. Co-observation of a variant of uncertain significance in BRCA1, BRCA2, or PALB2 with a pathogenic variant in another breast cancer gene equated to supporting evidence against pathogenicity following criterion strength assignment based on the likelihood ratio and showed utility in reclassification of missense BRCA1 and BRCA2 variants identified in BRIDGES. Our approach has applicability for assessing the value of co-observation as a predictor of variant pathogenicity in other clinical contexts, including for gene-specific guidelines developed by ClinGen Variant Curation Expert Panels.

Cancer burden in individuals with single versus double pathogenic variants in cancer susceptibility genes

Purpose

As panel testing expands, more individuals with double pathogenic variants (DPVs) in cancer susceptibility genes are likely to be identified. Little is known about the effects of DPVs on cancer phenotype, although this information is crucial for genetic counseling and risk management. We sought to describe the cancer phenotype among individuals with DPVs in cancer susceptibility genes.

Methods

A retrospective study of individuals with DPVs identified through a single testing laboratory from 2012 to 2017 was conducted. DPV combinations were enumerated. For DPV gene combinations that occurred >10 times, cancer histories of individuals with DPVs were compared with cancer histories of controls with a single PV matched by gene.

Results

Among 644 individuals with DPVs, combinations that included the ATM, BRCA1, BRCA2, CHEK2, and PALB2 genes occurred >10 times. There were 8883 matched controls for a single PV in these genes. The median age of first cancer diagnosis was younger with ATM+CHEK2 (43), compared with ATM (47, P = .016) or CHEK2 (47, P = .015) alone. Similar findings were observed when comparing age at first breast cancer (BC) for the ATM+CHEK2 with single-gene controls. Individuals with 2 CHEK2 PVs also were younger at first cancer diagnosis (40) compared with single CHEK2 PV controls (47, P = .0038). This difference was not driven by age at first BC diagnosis among females.

Conclusion

Individuals with ATM+CHEK2 or 2 CHEK2 PVs have a greater cancer burden than single gene controls. These findings can be used to counsel individuals with DPVs and their families and inform cancer screening recommendations.

Co-Occurrence of Germline Genomic Variants and Copy Number Variations in Hereditary Breast and Colorectal Cancer Patients

Hereditary Breast and Ovarian Cancer (HBOC) syndrome is an autosomal dominant disease associated with a high risk of developing breast, ovarian, and other malignancies. Lynch syndrome is caused by mutations in mismatch repair genes predisposing to colorectal and endometrial cancers, among others. A rare phenotype overlapping hereditary colorectal and breast cancer syndromes is poorly characterized. Three breast and colorectal cancer unrelated patients fulfilling clinical criteria for HBOC were tested by whole exome sequencing. A family history of colorectal cancer was reported in two patients (cases 2 and 3). Several variants and copy number variations were identified, which potentially contribute to the cancer risk or prognosis. All patients presented copy number imbalances encompassing PMS2 (two deletions and one duplication), a known gene involved in the DNA mismatch repair pathway. Two patients showed gains covering the POLE2 (cases 1 and 3), which is associated with DNA replication. Germline potentially damaging variants were found in PTCH1 (patient 3), MAT1A, and WRN (patient 2). Overall, concurrent genomic alterations were described that may increase the risk of cancer appearance in HBOC patients with breast and colorectal cancers.

A novel BRCA1 splicing variant detected in an early onset triple-negative breast cancer patient additionally carrying a pathogenic variant in ATM: A case report

The widespread adoption of gene panel testing for cancer predisposition is leading to the identification of an increasing number of individuals with clinically relevant allelic variants in two or more genes. The potential combined effect of these variants on cancer risks is mostly unknown, posing a serious problem for genetic counseling in these individuals and their relatives, in whom the variants may segregate singly or in combination. We report a female patient who developed triple-negative high grade carcinoma in the right breast at the age of 36 years. The patient underwent bilateral mastectomy followed by combined immunotherapy and chemotherapy (IMpassion030 clinical trial). Two years later she developed a skin recurrence on the right anterior chest wall. Despite intensive treatment, the patient died at 40-year-old due to disease progression. Gene panel testing of patient's DNA revealed the presence of a protein truncating variant in ATM [c.1672G>T; p.(Gly558Ter)] and of a not previously reported variant in the BRCA1 exon 22 donor splice site [c.5406+6T>C], whose clinical significance was unknown. The analysis of patient's RNA revealed the up-regulation of two alternative BRCA1 mRNA isoforms derived from skipping of exon 22 and of exons 22-23. The corresponding predicted protein products, p.(Asp1778GlyfsTer27) and p.(Asp1778_His1822del) are both expected to affect the BRCA1 C Terminus (BRCT) domain. The two variants were observed to co-occur also in the proband's brother who, in addition, was heterozygous for a common variant (c.4837A>G) mapped to BRCA1 exon 16. This allowed to ascertain, by transcript-specific amplification, the lack of functional mRNA isoforms expressed by the c.5406+6T>C allele and provided evidence to classify the BRCA1 variant as pathogenic, according to the guidelines of the Evidence-based Network for the Interpretation of Germline Mutant Alleles (ENIGMA) consortium. To our knowledge, excluding two cases detected following the screening of population specific recurrent variants, only one ATM/BRCA1 double heterozygote has been reported in the literature, being the case here described the one with the youngest age at cancer onset. The systematic collection of cases with pathogenic variants in more than one cancer predisposition gene is needed to verify if they deserve ad hoc counseling and clinical management.

Concurrent Pathogenic Variants of BRCA1, MUTYH and CHEK2 in a Hereditary Cancer Family

Concurrent pathogenic variants (PVs) in cancer predisposition genes have been reported in 0.1-2% of hereditary cancer (HC) patients. Determining concurrent PVs is crucial for the diagnosis, treatment, and risk assessment of unaffected family members. Next generation sequencing based diagnostic tests, which are widely used in HCs, enable the evaluation of multiple genes in parallel. We have screened the family members of a patient with bilateral breast cancer who was found to have concurrent PVs in BRCA1 (NM_007294.3;c.5102_5103del, p.Leu1701Glnfs*14) and MUTYH (NM_001128425.1;c.884C>T, p.Pro295Leu). Further analysis revealed concurrent PVs in CHEK2 (NM_007194.4;c.1427C>T, p.Thr476Met) and MUTYH (NM_001128425.1;c.884C>T, p.Pro295Leu) in the maternal uncle of the index case. Eight additional family members were found to have PVs in BRCA1 and MUTYH among 26 tested relatives. The sister and the brother of the index case who were diagnosed with breast and colon cancers, respectively, presented with the same genotype as the index case. Each family member was evaluated individually for clinical care and surveillance. This is the first report describing a family with BRCA1, MUTYH and CHEK2 concurrent PVs. Our findings provide valuable information for the assessment and management considerations for families with concurrent PVs.

Exome sequencing identifies RASSF1 and KLK3 germline variants in an Iranian multiple-case breast cancer family

Breast cancer is the most frequent malignancy among women in both developed and developing countries. Although several genes have been identified to harbor germline variants contributing to breast cancer risk, much of the heritability for breast cancer is yet undefined. In the present study, we have performed exome sequencing to detect susceptibility genes in an Iranian family with five first-degree family members affected with breast cancer. We identified novel candidate variants with predicted pathogenicity in RASSF1, KLK3 and FAM81B. The RASSF1 and KLK3 variants, but not the FAM81B variant, partially co-segregated with disease in the investigated pedigree and were not found in additional screenings outside the specific family. RASSF1 p.S135F is a missense substitution abolishing the ATM phosphorylation site, and KLK3 variant p.M1? is a deletion at the initiation codon that is predicted to abolish translation to the functional kallikrein protease, PSA. Our study suggests germline variation in RASSF1 and KLK3 as candidate contributors to familial breast cancer predisposition and illustrates the difficulties to determine the causal genetic risk factor among novel variants restricted to a single family.