Abstract P6-08-03: Germline mutational landscape in 5422 individuals at risk for hereditary breast and ovarian cancer who underwent multi-gene panel testing

Background: The introduction of multi-gene panel testing and improved awareness under patients and physicians has led to an increase of individuals with known germline pathogenic variants in hereditary breast and ovarian cancer (HBOC) genes. Significant regional differences exist in germline mutational landscape. We aimed to report the findings from multi-gene panel testing in a large Belgian cohort of individuals at risk for HBOC. Methods: All individuals who underwent multi-gene panel testing for HBOC at the Center for Human Genetics of the University Hospitals Leuven since the introduction of the panel were included (March 2016-April 2019). All included individuals were considered candidates for HBOC-panel testing by the requesting physician based on a personal or familial history of breast and/or ovarian cancer. Testing criteria from the Belgian Society of Human Genetics (www.beshg.be/download/guidelines/Guidelines_HBOC_2018.pdf) were met in the vast majority. The panel used was the BRCA Hereditary Cancer MASTR Plus® (Agilent, Belgium), with sequencing of BARD1, BRCA1, BRCA2, BRIP1, RAD51C, RAD51D, TP53, MRE11A, RAD50, NBN, FAM175A, ATM, PALB2, STK11, MEN1, PTEN, CDH1, MUTYH, CHEK2, BLM, XRCC2, EPCAM, MLH1, MSH6, PMS2 and MSH2. Sequencing was performed by NGS on a Miseq platform (Illumina). Genomic deletions and duplications in BRCA1 and BRCA2 were investigated with multiplex ligation-dependent probe amplification. We hereby report on the frequency of pathogenic and likely pathogenic germline variants in this population. Results: In 5422 individuals who underwent multi-gene panel testing, we detected 665 pathogenic or likely pathogenic variants in 639 patients (11,7%). In 25 patients (0.46%), more than one relevant alteration was detected with double heterozygosity in 24 individuals and triple heterozygosity in one. Germline variants in BRCA1 and BRCA2 were detected in 178 (3.3%) and 144 (2.7%) patients, resulting in a fraction of 26,4% and 21,4% of detected variants respectively. Relevant alterations in CHEK2, ATM, PALB2 and TP53 were observed in 135 (2.5%), 93 (1.7%), 26 (0.5%) and 11 (0.2%) patients respectively, accounting together for 39.3% of detected variants. Alterations in BRIP1/RAD51C/RAD51D were retrieved in 64 patients (1.2%) and alterations in mismatch-repair genes MSH6/MLH1/PMS2/MSH2 were detected in 0.3% of patients. These patients where dominantly referred for familial history of ovarian cancer. Furthermore, germline alterations in PTEN, CDH1 and BLM were observed in 3, 2 and 1 cases respectively. Double heterozygosity for ATM+CHEK2 and for ATM+BRCA2 were both observed in 3 cases. In the patient with triple heterozygosity, co-occurrence of pathogenic variants in BRCA2, ATM and CHEK2 was detected. Conclusions: In a large Belgian cohort of 5422 individuals at risk for HBOC who underwent multi-gene panel testing, a pathogenic or likely pathogenic germline variant was detected in 11,7% of patients, and in 0,46% of patients double or triple heterozygosity for HBOC-variants was observed. Almost 40% of detected variants were alterations beyond BRCA correlated with hereditary breast cancer (CHEK2, ATM, PALB2 and TP53). Given the time-lag to predictive testing in families, a significant rise in healthy carriers with these non-BRCA alterations is expected in the upcoming years. Citation Format: Kevin Punie, Griet Hoste, Griet Van Buggenhout, Ellen Denayer, Hilde Brems, Hilde Peeters, Ann Smeets, Ines Nevelsteen, Patrick Neven, Jan Ardui, Renate Prevos, Machteld Keupers, Chantal Van Ongeval, Giuseppe Floris, Christine Desmedt, Hans Wildiers, Genevieve Michils, Hilde Van Esch, Eric Legius. Germline mutational landscape in 5422 individuals at risk for hereditary breast and ovarian cancer who underwent multi-gene panel testing [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P6-08-03.