Laboratory cross-comparison of tumor BRCA1/2 analysis in a multicenter epithelial ovarian cancer series: The BORNEO GEICO60-0 study.

Abstract

6055 Background: Epithelial ovarian cancer (EOC) identification of BRCA1 and BRCA2 mutations is usually carried out in germline, representing around 17% in high grade serous ovarian cancer (HGSOC) and further 5-7% are only identified in the tumor (somatic). The aim of this study was to identify in EOC tumor BRCA mutation frequency and inter-laboratory reproducibility using different Next-generation Sequencing (NGS) approaches. Methods: In an ambispective study design, a population of unselected consecutive non mucinous EOC was clinically annotated and Formalin-Fixed Paraffin-Embedded (FFPE) tumor BRCA1/2 mutation analysis was undertaken in two laboratories (Lab-1 and Lab-2) simultaneously. Both laboratories used their own validated NGS panels; variant allele frequency threshold was 5% for single nucleotide polymorphism and 10% for indels. Each laboratory classified variants into three categories based on ACMG criteria: non-mutated (class 1-2), Variants of Uncertain Significance (VUS: class 3) and likely pathogenic/pathogenic (class 4-5). Germline BRCA analysis was available according to local clinical practice or centralized in Lab-1 if histology was low grade. Results: Ninety FFPE samples were received, 8 had insufficient material to be analyzed in both laboratories and 6 cases were discarded due to tumor cellularity below 20% leaving 76 cases to be sequenced. The population had a median age of 58 (25-84) years, 87% (66/76) of HGSOC histology and 70% of advanced stages (III-IVB: 53) and 14.5% (11) germline BRCA mutations (3 with not available results). Lab-1 identified 17 class 4-5 mutations, 11 correspond to germline, 4 (5.3%) are just somatic and 2 have germline results not available yet. Lab-2 had one not valuable analysis and identified 16 class 4-5 mutations, 10 corresponding to germline and 4 somatic variants. Percentage of concordance between both laboratories was 96% (kappa coefficient 0.883; p value < 0.0001). Three discordant out of 18 class 4-5 mutations included 2 undetected (VAF of 14.9% and 60.3% respectively) and one class 4 in Lab-2 classified as VUS in Lab-1 due to different interpretation criteria. Conclusions: The global BRCA mutation frequency in our series was 22.3% for Lab-1 and 21.0% for Lab-2. Concordance between tumor BRCA mutation analysis was high (96%). Nevertheless, further effort is required on harmonizing the technical and analytical aspects in tumor mutational analysis.