Abstract PS16-12: Double heterozygous pathogenic variants prevalence in a cohort of hereditary breast cancer patients
Authors: Megid Thais , Achatz Maria Isabel , Pisani Janina Pontes , Cartaxo Mariana 
Published: February 2021

Significant progress has been made in the identification of inherited genetic factors underlying hereditary cancers. Inherited pathogenic variants in cancer predisposition genes that confer moderate to high risk of breast cancer (BC) are found in 10% of BC cases. Pathogenic variants in BRCA1 and BRCA2 genes are the underlying alterations in hereditary BC. Women with a pathogenic variant in BRCA1 or BRCA2 are at substantially higher risk of developing breast, ovarian and pancreatic cancers and represent 25-28% of hereditary BC cases. The gold standard for molecular diagnosis of a hereditary cancer syndrome is aNext Generation Sequencing (NGS) panel that includes all genes known to confer moderate to high-risk for BC (TP53, PTEN, CHEK2, ATM, PALB2 STK11, RAD51C and BRIP1). Identifying who is eligible to perform genetic testing remains a challenge but presently age at the time of tumor diagnosis, family history and disease stage are still the best predictors. The identification of a germline pathogenic variant enables appropriate genetic counseling, risk-reducing interventions. The detection of variants in BRCA1, BRCA2 and PALB2 may also determine treatment options in patients with advanced or metastatic disease. The known non-BRCA1/2-associated hereditary BC comprise a heterogeneous group of tumors, for most of which the prevalence of histologic and immunohistochemical (IHQ) phenotypes are yet to be identified while triple-negative BC is the most prevalent in BRCA1 carriers. The co-occurence of more than one germline pathogenic variant in BC genes is a rare event and it may affect cancer risk and penetrance is still unknown. Only a few reports on cases and series of double mutation carriers have been described in BRCA1, BRCA2, PALB2, CHEK2, BLM or NBN. In this series case we report patients with double heterozygous (DH) mutation in BC, their age at diagnosis, presence of second neoplasia and cancer phenotype in moderate and high penetrance genes on germline panels. Considering this scenario, we performed an active search among the 2651 women from the Hereditary Cancer Registry at Hospital Sirio-Libanes, São Paulo, Brazil, between January 2013 and June 2020. We have included 229 patients with a histopathological confirmation of a BC who have tested positive for pathogenic/likely pathogenic variant. Of these, 4,3% (10/229) women were identified with DH mutation in high and moderate penetrance genes in BC (table 1). All patients carried a germline pathogenic variant in at least one high-penetrance gene. A total of 7 cases (7/10) carried at least one BRCA1/2 pathogenic variant. Two women (2/10) included had developed bilateral BC. The occurrence of a second primary cancer was described in three patients (3/10). The median age at first BC diagnosis was 36,7 years old. Two BC were found to be triple negative, five cases were of Luminal subtype and one was HER2+. The age at diagnosis is similar to most hereditary BC related to those developed by BRCA1 and TP53 germline variant carriers. In this case series there is no evidence of additive effect on the risk of tumor development. Larger series of DH mutation carriers are needed to estimate the risk in double heterozygous populations and to determine whether the presence of DH have a synergistic interaction or additive effect on cancer risk.

Table1 - Breast Cancer double variantsBreast Cancer double VariantsGeneVariantAge of Breast Cancer onset IHQ statusBilateral BCOther prymary neoplasia (age)BRCA1c.5266dupC36 yoER- PR- HER2 +YesPancreas (40), Lung (53)TP53c.1010G&gt;ABRCA1c.4165.4166delAG32yoN/ANoBreast (37), Skin (50)PALB2c.1240C&gt;TBRCA1c.5266dupC33yoER - RP- HER2 -NoNoATMc.6729_6730delAABRCA1c.3748G&gt;T33yoER- PR -HER2-NoNoRECQL4c.1568_1573delinsCCCCCBRCA2c.2516dupA49yoER+ PR+ HER2 -NoNoPMS2c.2182_2184delinsGBRCA2c.8960del32yoER+ PR+ HER2-NoNoATMc.901+1G&gt;ABRCA1c.1687C&gt;T38yoER+NoBreast Cancer (58)NBNc.1142delC PR +MUTYHc.536A&gt;G Her2-TP53c.1010G&gt;A35yoN/ANoNoMUTYHc.1187G&gt;AATMc.4906C&gt;T42yoER+NoNoTP53c.1010G&gt;APR+HER2-PALB2c.2711G&gt;A37yoER+yesNoCHEK2c.319+2T&gt;APR+HER2-BRCA2c.8960del32yoER+ PR+ HER2-NoNo

Citation Format: Thais Megid, Maria Isabel Achatz, Janina Pontes Pisani, Mariana Cartaxo. Double heterozygous pathogenic variants prevalence in a cohort of hereditary breast cancer patients [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS16-12.