Abstract PO4-16-01: EZH2 is Overexpressed in Invasive Carcinoma and DCIS in both BRCA1 and BRCA2 Mutation Carriers
Authors: Domingos Tabata Alves , Peixoto Roberto Bonfim Pimenta , Abreu Rodrigo Fonseca , Patel Ashka , Taneja Krishan , Moore McKenna , Kleer Celina , Dillon Deborah 
Published: May 2024

Abstract
Background
The transcriptional repressor EZH2 (Polycomb Group Protein Enhancer of Zeste Homologue 2) is overexpressed in multiple neoplasms including breast cancer where it associates with high proliferation, aggressive features and poor prognosis and is of interest as a potential therapeutic target. EZH2 nuclear expression in breast cancer has been shown to correlate specifically with high tumor grade and basal-like histologic features but has not been well studied in cancers from BRCA carriers. Here we evaluate the expression of EZH2 protein in BRCA-associated invasive breast carcinomas and precursor lesions.
Methods
Eighteen cases of invasive breast cancer in consented BRCA carriers (8 BRCA1 and 10 BRCA2) treated at Dana Farber Cancer Institute from 2001-2019 were reviewed by two pathologists (TAD and RBPP). Histopathologic features (histologic subtype, nuclear grade, mitotic score) and presence of precursor lesions were recorded. Immunohistochemistry for EZH2 was performed on freshly cut formalin-fixed paraffin-embedded tissue sections (1-3 sections/case) using a monoclonal antibody against EZH2 (D2C9, Cell Signaling). Nuclear EZH2 expression was scored as negative (score=1, no staining); weak (score 2, &lt; 25%); moderate (score=3, 25–75%); and strong (score=4, &gt;75%), of any intensity following published criteria. EZH2 overexpression was defined as scores 3 and 4.
Results
The majority of the invasive carcinomas showed grade III histology (13/18, 72%), as expected. Of 8 BRCA1 cases, 6 were classified as grade III (75%), 1 as grade II, and 1 as grade I (7 cases of invasive ductal carcinoma and 1 case of invasive tubular carcinoma). Of 10 BRCA2 cases, 7 were classified as grade III (70%) and 3 as grade II (30%) (5 cases of invasive ductal carcinoma and 5 cases of invasive carcinoma with ductal and lobular features). The majority of cases (13 of 18, 72%) showed high expression of EZH2 in the invasive carcinoma (6 BRCA1 and 7 BRCA2 cases; 2 grade II and 11 grade III). Of 13 cases with EZH2 overexpression, 6 were ER+/PR+/HER2- and 7 were triple negative, with 9 invasive ductal carcinomas and 4 invasive carcinomas with ductal and lobular features. Of 5 cases with no/low EZH2 overexpression, 1 was ER+/PR+/HER2-, 3 were ER+/PR-/HER2- and 1 was triple negative, with 3 invasive ductal carcinomas, 1 invasive carcinoma with ductal and lobular features and 1 invasive tubular carcinoma. In all cases with adjacent ductal carcinoma in situ (DCIS) (n=14), the pattern of EZH2 expression in the DCIS was identical to that seen in the invasive carcinoma (11 high and 3 low expression). Overexpression of EZH2 was not observed in any other precursor lesions (LCIS, ADH, ALH) or in normal tissue.
Conclusion
EZH2 protein overexpression is seen in the majority of invasive carcinomas in BRCA carriers, both in BRCA1 and in BRCA2. In all cases, the associated DCIS shows the same pattern of expression as the invasive carcinoma, suggesting that overexpression occurs early in tumorigenesis, while tumor cells are still confined within the ducts. The high rate of overexpression of EZH2 in BRCA1- and BRCA2-associated tumors suggests a potential role for EZH2 as a target and/or a biomarker in these cancers.
Citation Format: Tabata Alves Domingos, Roberto Bonfim Pimenta Peixoto, Rodrigo Fonseca Abreu, Ashka Patel, Krishan Taneja, McKenna Moore, Celina Kleer, Deborah Dillon. EZH2 is Overexpressed in Invasive Carcinoma and DCIS in both BRCA1 and BRCA2 Mutation Carriers [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-16-01.