# BRCA1 promoter hypermethylation is not associated with germline variants in Polish breast cancer patients

## TL;DR

This study found that a specific genetic variant in the BRCA1 gene is not linked to BRCA1 methylation or breast cancer risk in Polish patients, but may be associated with certain cancer types and metastases.

## Contribution

The study identifies a new genetic variant in the BRCA1 promoter and explores its potential associations with breast cancer subtypes and metastases in a Polish population.

## Key findings

- The BRCA1 c.20 + 101 C/G variant (rs799905) was not significantly associated with BRCA1 methylation or breast cancer risk.
- A borderline association was found between rs799905 and triple-negative breast cancer and lymph node metastases.
- Among BRCA1 pathogenic variant carriers, the GG genotype was more frequent compared to non-carriers.

## Abstract

Methylation of BRCA1 has been associated with an increased risk of breast cancer and specific clinical characteristics of the disease. In the British population, the genetic alteration c.-107 A/T has been shown to cause allelic methylation, leading to familial breast and ovarian cancer. However, this variant has not been detected in Polish population. Nonetheless, other genetic variants may still be associated with BRCA1 methylation, highlighting the need for further research.

This study aimed to analyze BRCA1 promoter region to identify germline alterations associated with BRCA1 methylation in peripheral blood DNA. Additionally, the correlation between the detected variants and breast cancer incidence, as well as clinical characteristics, was assessed.

One hundred breast cancer patients with BRCA1 methylation were analyzed using pyrosequencing to quantify methylation levels. Immunohistochemistry (IHC) was performed on formalin-fixed paraffin-embedded (FFPE) tumor tissue samples from these patients to assess BRCA1 expression. In 47 patients with the highest BRCA1 methylation and decreased BRCA1 expression, Sanger sequencing was performed encompassing 643 bp of BRCA1 promoter to identify potential variants associated with methylation and/or breast cancer. A variant was identified and genotyped in multiple patient groups, including 336 BRCA1 methylation-positive women, 1898 unselected breast cancer cases, 2234 healthy controls, and 309 BRCA1 pathogenic variant (PV) carriers. Statistical analyses were performed using Fisher’s exact test and Chi-square test in Stata/IC version 16.1.

The study identified BRCA1 c.20 + 101 C/G (rs799905) in the promoter region of the gene. However, no significant association was found between rs799905 and BRCA1 methylation or breast cancer risk. Nevertheless, a borderline association was observed between rs799905 and the occurrence of triple-negative breast cancer (TNBC) (p = 0.048) as well as lymph node (LN) metastases (p = 0.046). Among BRCA1 PV carriers, the GG genotype was significantly more frequent, while the CC genotype was 10 times less common compared to non-carriers (p = 0.003).

Rs799905 variant is not associated with BRCA1 methylation breast cancer risk. However, it may be linked to the occurrence of TNBC and LN metastases. Additionally, rs799905 may be associated to some extent with BRCA1 PVs, though further research is needed to clarify the nature of this potential correlation.