The tumor suppressor gene BRCA2 encodes the BRCA2 protein, which is involved in many cellular processes but exerts its primary role in the repair of double-stranded breaks (DSBs) via the homologous recombination pathway.

Pathogenic variants in BRCA2 are a major driver of cancer pathogenesis, especially in the breast, ovaries, and prostate. Germline pathogenic variants give rise to an increased lifetime risk of developing cancer.

BRCA2 is located at chromosome 13q12, encoding a 3.418aa large protein. The majority of the pathogenic variants are associated with cancer are located in exon 11 of the gene. BRCA2 is expressed in a variety of tissues but at higher rates in the breast and thymus and lower rates in the lung, ovary, and spleen.

BRCA2 and BRCA1

BRCA2 and BRCA1 are both involved in the DNA damage response of the cell, maintaining genome integrity and regulating progression in the cell cycle. Both function as tumor suppressor genes.

The DNA damage response includes five major pathways: Nucleotide Excision Repair (NER), Base Excision Repair (BER), Mismatch Repair (MMR), Homologous Recombination (HR), and Non-Homologous End-Joining (NHEJ). BRCA2 and BRCA1 both play major roles in repairing double-stranded DNA breaks (DSBs) through HR, thereby maintaining genomic integrity.

BRCA1 is also involved in the protection of stalled replication forks and the regulation of cell cycle checkpoints. The main role of BRCA2 in DSB repair is promoting the displacement of the ssDNA-binding protein RPA by RAD51 and the formation and stabilization of RAD51 nucleofilaments before homology search and strand invasion. Further, the poly(ADP-ribose) polymerase (PARP) creates poly(ADP-ribose) structures (PARylation) at sites of DNA damage.

BRCA2 then binds these PARylation structures, recruits other DNA-repair factors to the site, and acts as a scaffold for them. BRCA2 is also suggested to protect stalled replication forks through its interactions with PALB2 and RAD51. 
In cells that are deficient in BRCA1 or BRCA2, DSBs are repaired through the error-prone NHEJ rather than the high-fidelity HR pathway.

This leads to an accumulation of DNA errors and genomic instability. Germline mutations in the BRCA1 and BRCA2 genes can function as the first hit in Knudson’s two-hit model of cancer development. Promoter hypermethylation often acts as the second hit.

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The BRCA2 gene in breast cancer and ovarian cancer

Breast cancer is one of the most common cancers in women globally, accounting for approx. 7% of all cancer-related deaths in women. Ovarian cancer is a common cause of death in gynecological cancers.

This is especially due to the lack of early-stage symptoms and effective screening methods, leading to ~70% of patients presenting with advanced disease at diagnosis. Both germline and somatic mutations in the BRCA2 gene can give rise to the development of cancer.

Germline mutations in BRCA2 may lead to hereditary breast and ovarian cancer syndrome, which increases the lifetime risk of developing breast and ovarian cancer. This syndrome accounts for 5-7% of all breast cancer cases.

Patients with BRCA1 mutations have a 50-80% lifetime risk of breast cancer and a 30-50% risk of ovarian cancer, while BRCA2 pathogenic variant carriers have a lifetime risk of 40-45% and 15-30%, respectively.

Additionally, hereditary breast and ovarian cancer patients have an increased cancer susceptibility towards other specific cancer types, with a higher risk of developing pancreatic, gastric, fallopian tube, and prostate cancer. 

BRCA2 mutations are associated with an earlier breast cancer age of onset than the general population. BRCA2-mutated ovarian cancer is typically associated with high-grade serous carcinomas, presenting with higher grade, poor differentiation, higher mitotic index, and severe nuclear atypia compared to BRCA1 and BRCA2 wildtype ovarian cancer.

Breast cancers with a BRCA1 mutation are more frequently high-grade and triple-negative. BRCA2-mutated breast cancer, on the other hand, typically presents as isolated ductal carcinoma in situ.

In 2019, the US Preventive Services Task Force released a recommendation statement regarding risk assessment and testing for BRCA mutation-related cancer.

The process of investigating BRCA-related cancer involves three steps: risk assessment at the primary clinician, genetic counseling, and genetic testing. At the risk assessment, patients with a medical or family history of BRCA1 or BRCA2 mutations, or of breast cancer, ovarian cancer, tubal cancer, and/or peritoneal cancer are identified.

The clinicians can then use an appropriate risk assessment tool, such as the Manchester Scoring System or the Pedigree Assessment Tool, to determine whether to refer the patient to genetic counseling. Genetic counseling includes a more in-depth evaluation of the family history for risk assessment.

It is also a discussion of options, benefits, and potential harm, education of the patient, and interpretation of results of genetic testing. Genetic testing begins with the identification of any clinically significant mutation in the family, by testing a relative with a known BRCA-related cancer.

If a harmful BRCA1 or BRCA2 mutation is identified, the care for the patient consists of a variety of interventions to lower the cancer risk.

This includes intensive screening, risk-reducing medications, and risk-reducing mastectomy (RRM) and/or salpingo-oophorectomy. Risk-reducing medications include tamoxifen and the oral contraceptive pill.

Bilateral RRM (BRRM) is typically an option for patients with pathologic mutations in BRCA1 or BRCA2 with no prior history of breast cancer. After primary breast cancer, women are at a higher risk of developing a second primary, contralateral breast cancer. Therefore, contralateral RRM (CRRM) can be used to prevent a second breast cancer.

Interestingly, women with BRCA1 or BRCA2 mutations who had salpingo-oophorectomy, have a reduced risk of developing both breast and ovarian cancer.

BRCA2 methylation

The functional significance of BRCA2 promoter methylation in cancer has not yet been fully elucidated. In contrast to BRCA1, the methylation of BRCA2 is not currently considered a leading cause of BRCA2 deficiency and carcinogenesis.

Despite a recent increased focus on the role of BRCA2 methylation, a generalization of findings is difficult due to differences in methodologies and study populations. The main focus has been on the role of BRCA2 hypermethylation in BC and OC.

One report investigated the BRCA2 promoter methylation in the peripheral blood of healthy women and ovarian cancer patients without BRCA1 or BRCA2 mutation but found no difference in BRCA2 promoter methylation in the two groups.

Another cohort of ovarian cancer patients was followed for 54 months where BRCA2 promoter methylation was seen in 98.7%. However, these data did not correlate with protein expression levels, as 49.3% of the patients were positive for BRCA2 expression.

Multiple studies comparing normal and cancerous breast tissue from sporadic cancer patients have found BRCA2 promoter hypermethylation and a negative correlation between BRCA2 methylation and transcription levels.

In one of these studies, BRCA2 hypermethylation was associated with prolonged survival. BRCA2 promoter hypermethylation was found in at least 50% of both ductal carcinomas in situ and invasive ductal carcinoma cases. However, BRCA2 promoter methylation varies depending on the specific CpG sites investigated.

BRCA2 promoter hypermethylation may also play a role in other cancers, as seen in non-small cell lung cancer (NSCLC), where BRCA2 promoter methylation is detected in ~44% of the tumor tissue.

Additionally, BRCA2 promoter hypermethylation is suggested to be a viable biomarker for the leukemic transformation of myeloproliferative neoplasms.

Here, BRCA2 hypermethylation was associated with a decrease in mRNA and protein levels and an increase in olaparib sensitivity.

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How MethylDetect can assist you in your research

At MethylDetect, we can provide you with ready-to-use kits for DNA methylation analysis of your target of interest. In our catalog, we offer more than 850 EpiMelt assays.

In Products, you will find EpiMelt kits targeting genes relevant for BRCA2 research, such as, but not limited to, BRCA1, BRCA2, PALB2, RAD51, and ATM.
The EpiMelt assay kits are based on the Methylation-Sensitive High-Resolution Melting (MS-HRM) technology and can be used with standard laboratory equipment for qPCR and melting assessment.

Each EpiMelt assay kit comes with a unique control system, securing high sensitivity. Please consult our catalog at Products, and the protocol at Assay Protocol MethylDetect, for further information on setting up the EpiMelt analysis in your laboratory.

Custom-Tailored EpiMelt Kits

If your target gene is not found in our portfolio, we offer to design and produce EpiMelt assay kits tailored to target specific areas of the genome.

Following methylation-specific array screening analyses, you may have identified targets, which are not yet described in the literature.

In collaboration with you, we can design and produce EpiMelt assay kits targeting these specific genomic areas, and tailor the kit to fulfill your needs. We take into account if your samples are FFPE tissue, liquid biopsies, or high-quality DNA. Customer-tailored EpiMelt assays are always performed in close collaboration with you.

For further information, please contact us on info@methyldetect.com

Further reading

Carbine, N. E., Lostumbo, L., Wallace, J., & Ko, H. (2018). Risk-reducing mastectomy for the prevention of primary breast cancer. Cochrane Database Syst Rev, 4(4), Cd002748.

Daly, M. B., Pal, T., Berry, M. P., Buys, S. S., Dickson, P., Domchek, S. M., Elkhanany, A., Friedman, S., Goggins, M., Hutton, M. L., Karlan, B. Y., Khan, S., Klein, C., Kohlmann, W., Kurian, A. W., Laronga, C., Litton, J. K., Mak, J. S., Menendez, C. S., . . . Dwyer, M. A. (2021). Genetic/Familial High-Risk Assessment: Breast, Ovarian, and Pancreatic, Version 2.2021, NCCN Clinical Practice Guidelines in Oncology. J Natl Compr Canc Netw, 19(1), 77-102.

Fradet-Turcotte, A., Sitz, J., Grapton, D., & Orthwein, A. (2016). BRCA2 functions: from DNA repair to replication fork stabilization. Endocr Relat Cancer, 23(10), T1-t17.

Hoang, L. N., & Gilks, B. C. (2018). Hereditary Breast and Ovarian Cancer Syndrome: Moving Beyond BRCA1 and BRCA2. Adv Anat Pathol, 25(2), 85-95.

Owens, D. K., Davidson, K. W., Krist, A. H., Barry, M. J., Cabana, M., Caughey, A. B., Doubeni, C. A., Epling, J. W., Jr., Kubik, M., Landefeld, C. S., Mangione, C. M., Pbert, L., Silverstein, M., Simon, M. A., Tseng, C. W., & Wong, J. B. (2019). Risk Assessment, Genetic Counseling, and Genetic Testing for BRCA-Related Cancer: US Preventive Services Task Force Recommendation Statement. Jama, 322(7), 652-665.

Varol, U., Kucukzeybek, Y., Alacacioglu, A., Somali, I., Altun, Z., Aktas, S., & Oktay Tarhan, M. (2018). BRCA genes: BRCA 1 and BRCA 2. J buon, 23(4), 862-866.

Xie, C., Luo, J., He, Y., Jiang, L., Zhong, L., & Shi, Y. (2022). BRCA2 gene mutation in cancer. Medicine (Baltimore), 101(45), e31705.