J. Kerkhof

Examining the Concordance of Detection of Hereditary Cancer Gene Variants Between Blood, Tumour, and Normal Tissue in Patients with High-Grade Serous Ovarian Carcinoma

Background/Objectives: Access to genetic counselling and BRCA1/2 germline testing is standard of care for patients with high-grade serous ovarian carcinoma (HGSOC). While tumour testing reliably detects pathogenic variants in hereditary cancer genes, it cannot distinguish somatic from germline variants. Concurrent testing of non-cancerous (normal) tissue obtained during surgery may improve triage for germline testing and clinical genetics referral. This study evaluated the concordance of inherited variant detection among tumour, normal tissue, and blood to determine whether archived normal tissue can reliably identify germline pathogenic variants. Methods: Patients with HGSOC who had a pathogenic variant identified by targeted Next Generation Sequencing (NGS) tumour testing and underwent germline hereditary cancer gene panel (HCP) testing between April 2019 and November 2020 were included. HCP testing was performed on formalin-fixed, paraffin-embedded normal tissue from the original resection. Variant results were compared across tumour, normal tissue, and germline (blood) samples to determine concordance, false-negative, and false-positive rates. Results: Forty-one patients had confirmed tumour variants in BRCA1/2 or other HCP genes. Of these, 24 harboured a corresponding germline pathogenic variant. Archived normal tissue was available for 23 of these 24 cases, and all germline variants were detected in normal tissue, showing 100% concordance. Among the 17 patients without germline variants, all corresponding normal tissue samples were negative, also demonstrating 100% concordance. No false positives or negatives were identified. Conclusions: NGS testing of normal tissue at surgical resection reliably identifies germline pathogenic variants in patients with HGSOC. Incorporating this approach may help triage patients for clinical genetics assessment.

Examining the Diagnostic Yield of Tumour Testing and Qualifying Germline Concordance for Hereditary Cancer Variants in Patients with High-Grade Serous Carcinoma

Despite advances in treatment, prognosis for most patients with high-grade serous carcinoma (HGSC) remains poor. Genomic alterations in the homologous recombination (HR) pathway are used for cancer risk assessment and render tumours sensitive to platinum-based chemotherapy and poly (ADP-ribose) polymerase inhibitors (PARPi), which can be associated with more favourable outcomes. In addition to patients with tumours containing BRCA1 or BRCA2 pathologic variants, there is emerging evidence that patients with tumours harbouring pathologic variants in other HR genes may also benefit from PARPi therapy. The objective of this study is to assess the feasibility of primary-tumour testing by examining the concordance of variant detection between germline and tumour-variant status using a custom hereditary cancer gene panel (HCP). From April 2019 to November 2020, HCP variant testing was performed on 146 HGSC formalin-fixed, paraffin-embedded tissue samples using next-generation sequencing. Of those, 78 patients also underwent HCP germline testing using blood samples. A pathogenic variant was detected in 41.1% (60/146) of tumours tested, with 68.3% (41/60) having either a BRCA1 or BRCA2 variant (n = 36), or BRCA1/2 plus a second variant (n = 5), and 31.2% (19/60) carrying a pathogenic variant in another HCP gene. The overall variant rate among the paired germline and tumour samples was 43.6% (34/78), with the remaining 56% (44/78) having no pathogenic variant detected in the germline or tumour. The overall BRCA1/2 variant rate for paired samples was 33.3% (26/78), with germline variants detected in 11.5% (9/78). A non-BRCA1/2 germline variant in another HCP gene was detected in 9.0% (7/78). All germline variants were detected in the tumour, demonstrating 100% concordance. These data provide evidence supporting the feasibility of primary-tumour testing for detecting germline and somatic variants in HCP genes in patients with HGSC, which can be used to guide clinical decision-making, and may provide opportunity for improving patient triage and clinical genetic referral practices.