FREQUENCY OF BRCA1 GENE PROMOTER HYPERMETHYLATION AND LOSS OF BRCA1 PROTEIN EXPRESSION IN SPORADIC BREAST CANCER

Abstract

Purpose/Objective: Methylation of the BRCA1 gene promoter region is associated with decreased BRCA1 protein
expression. The objective of the following study was to determine promoter methylation and loss of protein
expression in a small cohort of sporadic breast cancer cases.
Material/Methods: The study was reviewed by the ethics review committee at Forman Christian College. A
retrospective review of cases was performed to select those with specific morphological features suggestive of
BRCA1 promoter methylation. A total of 35 formalin fixed paraffin embedded (FFPE) tumor blocks were obtained
from the Histopathology Section, Chughtais Lahore Lab. Of these 30 were sporadic tumor samples, and 5 were
benign tumor samples. A tissue microarray containing samples from each tumor was prepared and stained for
BRCA1 using a commercially available monoclonal antibody against BRCA1 (Ab-1) clone MS110 (mAb). Each
IHC stain was reviewed independently by two pathologists and scored as absent, equivocal, or retained. DNA was
extracted from FFPE tumor samples, the DNA was modified using a bisulfite conversion kit and BRCA1 promoter
hypermethylation was detected using a methylation specific PCR.
Results: BRCA1 expression was absent in 76.6% of sporadic breast tumor samples (n=23/30), equivocal in 13.3%
samples (n=4/30) and retained in 10% of samples (n=3/30). Of the 23 samples (76.6%) that had loss of BRCA1
expression, methylation was positive in 82.6% (n=19) and methylation was negative in 21.7% (n=4). Of the 4
samples (13.3%) with equivocal BRCA1 expression, methylation was positive in 50% (n=2) and methylation was
negative in 50% (n=2). BRCA1 methylation was negative in all of the 10% samples with retained protein
expression.
Conclusion: The results from this study will provide valuable information regarding the role of epigenetic
modifications and BRCA 1 protein expression in breast cancer among Pakistani females. BRCA defective cancers
are highly susceptible to DNA damaging chemotherapeutic agents such as platinum analogs, therefore BRCA1
protein expression has an impact on prognosis and management of patients. IHC can be explored as a low cost
screening tool for detection of BRCA1 dysfunction, especially in our resource constrained setting.