Alleviating misclassified germline variants in underrepresented populations: A strategy using popmax.

PURPOSE: Germline variant interpretation often depends on population-matched control cohorts. This is not feasible for population groups that are underrepresented in current population reference databases. METHODS: We classify germline variants with population-matched controls for 2 ancestrally diverse cohorts of patients: 132 early-onset or familial colorectal carcinoma patients from Singapore and 100 early-onset colorectal carcinoma patients from the United States. The effects of using a population-mismatched control cohort are simulated by swapping the control cohorts used for each patient cohort, with or without the popmax computational strategy. RESULTS: Population-matched classifications revealed a combined 62 pathogenic or likely pathogenic (P/LP) variants in 34 genes across both cohorts. Using a population-mismatched control cohort resulted in misclassification of non-P/LP variants as P/LP, driven by the absence of ancestry-specific rare variants in the control cohort. Popmax was more effective in alleviating misclassifications for the Singapore cohort than the US cohort. CONCLUSION: Underrepresented population groups can suffer from higher rates of false-positive P/LP results. Popmax can partially alleviate these misclassifications, but its efficacy still depends on the degree with which the population groups are represented in the control cohort.

Whole-exome sequencing of BRCA-negative breast cancer patients and case-control analyses identify variants associated with breast cancer susceptibility.

BACKGROUND: For the majority of individuals with early-onset or familial breast cancer referred for genetic testing, the genetic basis of their familial breast cancer remains unexplained. To identify novel germline variants associated with breast cancer predisposition, whole-exome sequencing (WES) was performed. METHODS: WES on 290 BRCA1/BRCA2-negative Singaporeans with early-onset breast cancer and/or a family history of breast cancer was done. Case-control analysis against the East-Asian subpopulation (EAS) from the Genome Aggregation Database (gnomAD) identified variants enriched in cases, which were further selected by occurrence in cancer gene databases. Variants were further evaluated in repeated case-control analyses using a second case cohort from the database of Genotypes and Phenotypes (dbGaP) comprising 466 early-onset breast cancer patients from the United States, and a Singapore SG10K_Health control cohort. RESULTS: Forty-nine breast cancer-associated germline pathogenic variants in 37 genes were identified in Singapore cases versus gnomAD (EAS). Compared against SG10K_Health controls, 13 of 49 variants remain significantly enriched (False Discovery Rate (FDR)-adjusted p < 0.05). Comparing these 49 variants in dbGaP cases against gnomAD (EAS) and SG10K_Health controls revealed 23 concordant variants that were significantly enriched (FDR-adjusted p < 0.05). Fourteen variants were consistently enriched in breast cancer cases across all comparisons (FDR-adjusted p < 0.05). Seven variants in GPRIN2, NRG1, MYO5A, CLIP1, CUX1, GNAS and MGA were confirmed by Sanger sequencing. CONCLUSIONS: In conclusion, we have identified pathogenic variants in genes associated with breast cancer predisposition. Importantly, many of these variants were significant in a second case cohort from dbGaP, suggesting that the strategy of using case-control analysis to select variants could potentially be utilized for identifying variants associated with cancer susceptibility.

Germline Variants Associated with Nasopharyngeal Carcinoma Predisposition Identified through Whole-Exome Sequencing.

The current understanding of genetic susceptibility factors for nasopharyngeal carcinoma (NPC) is still incomplete. To identify novel germline variants associated with NPC predisposition, we analysed whole-exome sequencing data from 119 NPC patients from Singapore with a family history of NPC and/or with early-onset NPC, together with 1337 Singaporean participants without NPC. Variants were prioritised and filtered by selecting variants with minor allele frequencies of <1% in both local control (n = 1337) and gnomAD non-cancer (EAS) (n = 9626) cohorts and a high pathogenicity prediction (CADD score > 20). Using single-variant testing, we identified 17 rare pathogenic variants in 17 genes that were associated with NPC. Consistent evidence of enrichment in NPC patients was observed for five of these variants (in JAK2, PRDM16, LRP1B, NIN, and NKX2-1) from an independent case-control comparison of 156 NPC patients and 9770 unaffected individuals. In a family with five siblings, a FANCE variant (p. P445S) was detected in two affected members, but not in three unaffected members. Gene-based burden testing recapitulated variants in NKX2-1 and FANCE as being associated with NPC risk. Using pathway analysis, endocytosis and immune-modulating pathways were found to be enriched for mutation burden. This study has identified NPC-predisposing variants and genes which could shed new insights into the genetic predisposition of NPC.

Clinical characteristics and genetic testing outcome of suspected hereditary peripheral nerve sheath tumours in a tertiary cancer institution in Singapore.

BACKGROUND: Peripheral Nerve Sheath Tumors (PNST) are a diverse group of mostly benign tumours uncommon in the general population. About 5-10% of PNSTs are hereditary, predominantly arising from germline variants in NF1, NF2, SMARCB1, or LZTR1 gene. METHODS: We reviewed the clinical characteristics and genetic testing results of patients referred to the NCIS Adult Cancer Genetics Clinic for suspected hereditary PNST. RESULTS: 3,001 patients suspected to have various hereditary cancer syndromes were evaluated between year 2000 to March 2021. 13 (0.4%) were clinically diagnosed to have hereditary PNSTs. The majority were male (54%), with a median age at presentation to the genetics clinic of 29 years (range 19-48). 11/13 (85%) patients had multiple PNSTs, 12/13 (92%) had young onset PNSTs, 5/13 (38.5%) had personal and family history of PNST. 11/13 patients (85%) had clinical features of neurofibromatosis type 1 (NF1) including one patient who also fulfilled clinical criteria of neurofibromatosis type 2 (NF2); 2/13 (14%) had multiple schwannomas. Four patients underwent multi-gene panel testing, including one patient with clinical NF1, one patient who met both clinical NF1 and NF2 criteria, and two patients with multiple schwannomas. The patient with clinical features of NF1 was heterozygous for a pathogenic c. 2033dup variant in the NF1 gene. The patient with both NF1/NF2 features was heterozygous for a novel c.732 T > A nonsense variant in the NF2 gene. The two patients with multiple schwannomas were heterozygous for a pathogenic/likely pathogenic variant in the LZTR1 gene and are the first LZTR1-positive schwannomatosis patients reported in Asia. CONCLUSION: Hereditary PNSTs are rare referrals to an adult cancer genetics clinic. NF1 is the most common PNST seen. LZTR1 variants may be the underlying cause in Asian patients with multiple schwannomatosis.

Characteristics and genetic testing outcomes of patients with clinically suspected paraganglioma/pheochromocytoma (PGL/PCC) syndrome in Singapore.

BACKGROUND: Hereditary paraganglioma (PGL) and pheochromocytoma (PCC) syndromes are rare conditions, with limited data on spectrum of causative gene variants of these syndromes in Asian patients. METHODS: We describe the clinical characteristics and genetic testing outcomes of patients with suspected hereditary PGL/PCC who were referred to a tertiary cancer genetics clinic in Singapore. RESULTS: Among 2196 patients with suspected hereditary cancer syndrome evaluated at the cancer genetics clinic from 2000 to 2019, 13/2196 (0.6%) patients fulfilled clinical suspicion for hereditary PGL/PCC syndrome. After genetic counselling, 10 patients underwent multi-gene next generation sequencing and deletion/duplication analysis, including SDHAF2, SDHA, SDHB, SDHC, SDHD, VHL, NF1, RET, MAX, and TMEM127. Seven of 10 patients (70%) were identified to carry pathogenic variants, including 3 unrelated Chinese patients with head and neck PGL who carried the same SDHD: c.3G > C (p.Met1Ile) variant that was previously reported to be a possible founder variant in Chinese, and 3 patients with urogenital PGL and 1 patient with retroperitoneal PGL who carried different SDHB variants. Variant carriers were younger, more likely to present with multiple tumours, or have family history of paraganglioma or pheochromocytoma, than non- variant carriers. CONCLUSION: Hereditary PGL/PCC accounts for only 0.6% of patients seen in an adult cancer genetics clinic in Asia. SDHD and SDHB genes remain the most important causative genes of hereditary PGL/PCC in Asia even when patients are tested with multi-gene NGS panel.

Using next-generation sequencing (NGS) platform to diagnose pathogenic germline BRCA1/2 mutations from archival tumor specimens.

OBJECTIVE: Clinical genetic testing to diagnose germline mutations often requires blood sample or saliva smear from a cancer-affected individual. This rules out testing in families when cancer-affected individuals are deceased. We explored the use of a next-generation sequencing (NGS) platform to diagnose germline pathogenic mutations from tumors. METHODS: Archival tumors (ovarian = 26, breast = 25, others = 9) were retrieved from 60 cancer patients who have undergone multi-gene panel blood testing. Genomic DNA was extracted and sequenced for BRCA1/2 using a NGS platform. 41/60 specimens were sequenced for 5 other genes (APC, ATM, PALB2, PTEN, TP53). Tumor testing and results interpretation were performed blinded to the blood test result. RESULTS: All 38 patients with no BRCA1/2 mutations on blood testing were correctly tested negative on tumor. Tumor testing correctly diagnosed BRCA1/2 pathogenic mutations in 15/22 (68%) patients while in 7/22 (32%) patients, the mutation was either detected but incorrectly classified as VUS (n = 3) or not detected at all (n = 4). Overall concordance rate for tumor and blood testing for BRCA1/2 mutations was 88%, with 0% false positive and 32% false negative rate for pathogenic mutations. Tumor testing correctly diagnosed 1/2 pathogenic germline ATM mutation, 1/1 pathogenic germline PALB2 mutation and 2/2 pathogenic germline TP53 mutations. False positive germline mutations were diagnosed in 4 genes at a rate of 2.4%-10.3% (APC = 2.4%, PALB2 = 2.4%, PTEN = 4.9%, TP53 = 10.3%). CONCLUSION: Tumor testing for BRCA1/2 germline mutations using an NGS platform is fairly reliable with no false positive findings, and correctly diagnosed more than two-thirds of pathogenic germline BRCA1/2 mutations. However, it is not reliable to diagnose pathogenic germline mutations in genes frequently mutated in sporadic cancers, such as PTEN and TP53.

Next Generation Sequencing Reveals Novel Mutations in Mismatch Repair Genes and Other Cancer Predisposition Genes in Asian Patients with Suspected Lynch Syndrome.

BACKGROUND: Although at least 5 genes are implicated in Lynch Syndrome (LS), up to 50% of suspected cases are owing to undefined genes. We utilized next generation sequencing (NGS) to characterize the mutation profile of patients with cancer (CA) suspected to have LS. PATIENTS AND METHODS: We enrolled 174 Asian patients with CA from our CA Genetics Clinic from 2000 to 2014 suspected to have LS, and obtained germline DNA for NGS using TruSight Cancer. Frameshift, nonsense, and known deleterious mutations were considered pathogenic. Polymorphisms ≤ 1% frequency in 1000 Genomes (Asian) were classified using established databases. RESULTS: Of the 174 probands, 80.5% were Chinese, the median age at CA diagnosis was 45 years (range, 18-82 years), and 84.5% and 8.6% had colon and LS-like CA, respectively. Forty-seven of 100 evaluable colon CA probands had LS-like histopathologic features. Nineteen of 174 had family history fulfilling Amsterdam I/II Criteria, whereas the rest fulfilled Bethesda Guidelines. Thirty-one of 174 harbored pathogenic mutations with 10 in LS genes only, 20 in non-LS genes only, and 1 in both. Of the 11 with LS gene mutations, MLH1 was most commonly involved (n = 7), followed by MSH2, MSH6, and PMS2. Nine of 174 had pathogenic mutations diagnostic of alternative hereditary syndromes including 2 each in CDH1, APC, and BRCA1, and 1 each in BRCA2, SMAD4, and MUTYH. Ten unique mutations were detected in low-to-moderate penetrance genes: 6 individuals had a recurring novel KIT:c.2836C>T nonsense mutation (n = 3) or ERCC4:c.2169C>A nonsense mutation (n = 3) without LS gene mutation, which is of clinical interest. CONCLUSIONS: In this Asian study, NGS proved to be feasible in screening for causative mutations in patients with CA suspected to have LS.

Discoveries beyond BRCA1/2: Multigene testing in an Asian multi-ethnic cohort suspected of hereditary breast cancer syndrome in the real world.

BACKGROUND: Due to historically low uptake of genetic testing, the mutational spectrum of Asians with Hereditary Breast Cancer (HBC) is not well understood. This study sought to understand the incidence and spectrum of germline mutations in Asian patients with suspected HBC in a clinic setting. METHODS: 1056 patients with suspected HBC were seen in our Cancer (CA) Genetics Clinic from 2000-2017, of which 460 underwent genetic testing. RESULTS: Of 460 probands tested, 93% were female, 61% Chinese, 90% had prior CA, with 19% (77/414) having ≥2 primary CA. Median age at CA-diagnosis was 43y (17-83); 70% had Breast CA (BC) and 25% Ovarian CA (OC). 34% had young-onset BC, 8% bilateral BC, and 4% BC/OC. Majority had family history of BC (53%) or OC (20%). 57% underwent multigene testing (14-49 genes), 34% targeted testing, and 8% predictive testing. 30% were found to have a pathogenic mutation: 80% in BRCA1/2 (8 novel mutations noted). Of 33 non-BRCA1/2 pathogenic mutations detected, 61% were in 11 BC genes while 39% were in non-BC genes suggestive of alternative CA syndromes. Testing beyond BRCA1/2 impacted management for 15.9% (22/138) of carriers, but extensive testing identified variants of uncertain significance (VUS) in up to 44.5% of probands. Restricting multigene panel testing to a guideline-based 20-gene panel including Lynch Syndrome genes was found to be most optimal, detecting 94.6% of mutation carriers while reducing VUS rate to 21.5%. CONCLUSIONS: Evolution of CA Genetics testing strategy to a multigene approach facilitated detection of pathogenic mutations in non-BRCA1/2 genes and aided management. Guideline-based panel testing is feasible and can be offered in Asians with suspected HBC.

Clinical genetic testing outcome with multi-gene panel in Asian patients with multiple primary cancers.

BACKGROUND: Developing multiple cancers is an indicator of underlying hereditary cancer predisposition, but there is a paucity of data regarding the clinical genetic testing outcomes of these patients. METHODS: We compared cancer index patients with ≥2 primary malignancies versus 1 primary cancer who underwent clinical evaluation and testing with multi-gene panels comprising up to 49 genes from 1998-2016. RESULTS: Among 1191 cancer index patients, 80.6%, 17.2%, and 2.2% respectively had 1, 2, and ≥3 primary malignancies. For patients with 2 primary cancers (n=205), the most common cancer pairs were bilateral breast (37.5%), breast-ovary (11.7%), endometrium-ovary (9.2%), colon-endometrium (3.9%) and colon-colon (3.4%). 42.3% patients underwent gene testing including 110/231 (47.6%) with multiple malignancies. Pathogenic variants were found more frequently in younger patients, in those with a family history of cancer related to the suspected syndrome, and a trend towards significance in those with multiple primary cancers (35.5% vs. 25.6%, p = 0.09). In patients with multiple cancers, pathogenic variants were most commonly identified in BRCA1 (38.5%), BRCA2 (17.9%), and the mismatch repair genes (20.5%), while 23.1% of pathogenic mutations were in other moderate- to high-penetrance cancer predisposition genes including APC, ATM, MUTYH, PALB2, RAD50 and TP53. CONCLUSION: Patients with multiple cancers were more likely to carry pathogenic mutations than those with single cancer. About three-quarters of deleterious mutations in patients with multiple primary cancers were in BRCA1/2 and the mismatch repair genes, but multi-gene panel testing facilitated the detection of mutations in another 6 genes and is warranted in this high-risk population.