BRCA1 vs. BRCA2: What's the Difference?

01 / 09

What's the basic difference between BRCA1 and BRCA2?

BRCA1 and BRCA2 are separate genes on different chromosomes that both help repair DNA double-strand breaks through homologous recombination. A pathogenic variant in either gene raises cancer risk, but the specific cancers, the degree of risk, and the tumor biology differ by gene.^[1,2,7]

Despite the shared "BRCA" name, BRCA1 and BRCA2 encode entirely different proteins. As Dr. Susan Domchek of the Basser Center for BRCA has stated, "although these genes sound the same, they are completely different genes and they make completely different proteins."^[7]

BRCA1

Chromosome 17q21.31 · NCBI Gene 672

Promotes end resection at DNA break sites, directing repair toward homologous recombination rather than error-prone pathways. Also assists RAD51-mediated strand pairing.^[3,9]

BRCA2

Chromosome 13q13.1 · NCBI Gene 675

Loads RAD51 recombinase onto single-stranded DNA at break sites, forming the nucleofilament that carries out the central step of homologous recombination.^[4,9]

BRCA1 and BRCA2 work in a linked complex (BRCA1-PALB2-BRCA2) during DNA repair. A pathogenic variant in either gene disrupts this repair pathway, but the downstream consequences for cancer type and tumor behavior are not identical.^[9]

For a broader overview of both genes, including prevalence and who is most affected, see what BRCA1 and BRCA2 mean for cancer risk.

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02 / 09

How do cancer risks compare between BRCA1 and BRCA2?

Both BRCA1 and BRCA2 raise breast and ovarian cancer risk substantially, but the gene-specific profiles differ. BRCA2 carries a materially higher lifetime risk of prostate cancer (19 to 61% vs. 7 to 26% for BRCA1), pancreatic cancer (5 to 10% vs. up to 5%), and male breast cancer (2 to 7% vs. ~1%), while BRCA1 ovarian cancer risk runs higher than BRCA2 (39 to 58% vs. 13 to 29%).^[1,5,8]

Six cancer types with estimated risk for BRCA1 and BRCA2 carriers compared with the general population. Ranges reflect the NCI fact sheet (reviewed July 2024) unless noted; Basser Center and Kuchenbaecker et al. 2017 figures are included where they differ.

Cancer type	BRCA1 carriers	BRCA2 carriers	General population
Female breast, lifetime	60–72% (Basser)	55–69% (Basser)	~13%
Ovarian, lifetime	39–58%	13–29%	~1.1%
Male breast, by age 70	~1% (0.2–1.2%)	2–7% (1.8–7.1%)	~0.1%
Prostate, by age 80	7–26%	19–61%	~10.6%
Pancreatic, lifetime	Up to 5%	5–10%	~1.7%
Melanoma, lifetime	Evidence limited	2.3–5%	~1.5–2%

Breast cancer figures use Basser Center's gene-specific split (BRCA1 60 to 72%, BRCA2 55 to 69%) rather than Dana-Farber's combined "50 to 85% for both genes," because the split matters on a comparison page. Kuchenbaecker et al. 2017 reported 72% for BRCA1 and 69% for BRCA2 by age 80 in a prospective cohort of 9,856 carriers. Ovarian, prostate, pancreatic, and male breast figures are from NCI's consumer fact sheet (July 2024).^[1,5,8]

Why do published risk ranges vary by source?

Five documented reasons explain the differences:^[1,5,8,10]

Different underlying studies. Older clinic-ascertained cohorts (Antoniou 2003, Chen 2007) report lower figures than the larger prospective Kuchenbaecker 2017 cohort, which followed carriers recruited 1997 to 2011.
Different age cutoffs. "By age 70" and "by age 80" and "lifetime" produce different numbers for the same underlying risk.
Mutation position. Risk varies by where in the gene the variant falls. Variants at either end of BRCA1 raise breast risk more than ovarian risk; BRCA2 variants that do not truncate the protein carry lower ovarian risk (~3% vs. ~11%).^[10]
Consumer vs. professional summaries. NCI's own consumer fact sheet and its health-professional PDQ page give different figures for the same cancer (e.g., BRCA2 pancreatic: 5 to 10% on the fact sheet vs. 3 to 5% on the PDQ page), because they were last updated at different times.
Family history and other modifiers. Individual risk within these ranges depends on family history, other genetic variants, and environmental factors.^[5]

03 / 09

Do BRCA1 and BRCA2 tumors behave differently?

Yes. BRCA1-associated breast tumors are triple-negative in approximately 69% of cases (hormone-receptor-negative and HER2-negative), while BRCA2-associated breast tumors are hormone-receptor-positive (ER-positive) in approximately 70 to 80% of cases. This distinction affects what treatment options are typically considered.^[6,7,11]

Triple-negative breast cancer (TNBC) does not respond to hormone-blocking therapies such as tamoxifen or aromatase inhibitors and is generally treated with chemotherapy. BRCA2-associated tumors, because they are usually ER-positive, have a broader range of treatment options including hormonal therapy.^[6,11]

Dr. Susan Domchek of the Basser Center for BRCA describes BRCA1-associated breast cancers as "generally triple negative" and BRCA2-associated breast cancers as "generally estrogen receptor positive. Not always, but more often than not."^[7]

Receptor status comparison between BRCA1 and BRCA2 breast tumors.

Feature	BRCA1 tumors	BRCA2 tumors
ER-negative	~78%	~23%
Triple-negative	~69%	~16%
ER-positive	~22%	~77%

Percentages from NCI PDQ health-professional summary, based on carrier tumor series. Not every BRCA1 tumor is triple-negative, and not every BRCA2 tumor is ER-positive.^[6]

04 / 09

Is BRCA1 and BRCA2 inheritance different?

No. BRCA1 and BRCA2 pathogenic variants are inherited in the same autosomal dominant pattern, and a carrier of either gene has a 50% chance of passing the variant to each child. Both men and women can carry, inherit, and pass on a variant in either gene.^[1,2]

Autosomal dominant means the variant sits on a non-sex chromosome and needs only one altered copy to affect cancer susceptibility. The inheritance pattern does not differ between the two genes. A parent who carries a BRCA1 variant and a parent who carries a BRCA2 variant face the same 50% transmission probability per pregnancy.^[1,2]

The cancers that develop, and at what age they tend to appear, differ by gene. The probability that a child inherits the variant does not.^[1]

05 / 09

Does testing check both genes, or do I need to test for each separately?

Combined BRCA1 and BRCA2 analysis is the clinical default. Most hereditary cancer panels and whole-genome sequencing services analyze both genes together. Single-gene ordering exists at some laboratories (typically payer-driven), but it is not the standard first-line approach. A result will indicate whether either gene shows a pathogenic or likely pathogenic variant, a variant of uncertain significance, or no finding.^[1,2,12]

Major clinical laboratories (Myriad Genetics, Invitae/Labcorp, Ambry Genetics) include both BRCA1 and BRCA2 on their hereditary cancer panels, typically alongside other cancer-risk genes such as PALB2, CHEK2, and ATM. Ordering a "BRCA test" through any of these labs sequences both genes as a pair.^[12]

The one situation where a single-gene or single-variant test makes sense: when a specific pathogenic variant has already been identified in a family member. A targeted familial-variant test checks whether you inherited that exact change. It is faster, less expensive, and answers a narrower question.^[1,12]

Consumer tests such as 23andMe check a fixed list of 44 selected BRCA variants: 24 in BRCA1 and 20 in BRCA2, all single-nucleotide changes or small insertions/deletions (FDA 510(k) K223597, August 2023). A negative consumer result does not rule out the thousands of other known pathogenic variants in either gene, and the test does not detect large rearrangements, which account for up to one-third of pathogenic BRCA1 variants in some populations.^[12,13]

06 / 09

Does a BRCA1 or BRCA2 finding change what happens next?

The next steps after a positive BRCA result are largely similar for both genes: enhanced screening, discussion of risk-reducing options, and cascade testing of family members. The specific screening emphasis can differ by gene. BRCA2-positive men, for example, face a substantially higher prostate cancer risk and may begin PSA screening earlier than BRCA1-positive men.^[1,5,14]

Both BRCA1 and BRCA2 carriers typically qualify for breast MRI screening in addition to mammography, and both are candidates for discussion of risk-reducing mastectomy and/or oophorectomy. The gene-specific differences that matter for clinical management include:^[1,14]

Prostate screening intensity. NCCN recommends BRCA2 carriers consider PSA screening beginning at age 40, given the higher prostate cancer risk (19 to 61%) compared with BRCA1 carriers (7 to 26%).^[14]
Pancreatic cancer surveillance. BRCA2 carriers face a 5 to 10% lifetime pancreatic cancer risk. Screening eligibility depends on family history and is discussed on a case-by-case basis.^[1,14]
Tumor biology and treatment. The triple-negative vs. ER-positive distinction can inform treatment discussions if cancer develops, but treatment decisions belong with an oncology team.^[6]

For a detailed discussion of what to expect after a positive result, see what a positive BRCA result means for you. For male-specific risks and screening, see BRCA and cancer risk in men.

07 / 09

Common questions

Is BRCA1 or BRCA2 worse?

Neither gene is simply "worse." BRCA1 carries a somewhat higher ovarian cancer risk (39 to 58% vs. 13 to 29%), while BRCA2 carries higher prostate, pancreatic, and male breast cancer risk. BRCA1 tumors are more often triple-negative, which limits treatment options. BRCA2 tumors are more often hormone-receptor-positive, which broadens them. The better question is which specific risks each gene raises and what screening changes follow.^[1,5,7]

Can a DTC or at-home test tell me which gene I have a variant in?

Only if the test actually reports on that specific gene. 23andMe's current report checks 44 selected variants across both BRCA1 and BRCA2 and will name which gene a detected variant falls in. A negative result from this test means none of those 44 specific changes were found; it does not rule out the thousands of other known pathogenic variants in either gene. Clinical-grade testing sequences both genes completely and is the standard for definitive BRCA assessment. For more on who the three Ashkenazi founder variants affect, see the three Ashkenazi founder variants, explained.^[1,13]

08 / 09

Why whole-genome sequencing beats a narrow BRCA test, and where it doesn't

When a specific pathogenic variant has already been identified in a relative, a targeted single-variant test is the fastest, least expensive way to check your own status (see testing for a known family variant). Without a known family variant, broader testing makes sense: HLI's $599 whole-genome sequencing produces a cancer-risk assessment that covers BRCA1 and BRCA2 among other genes, alongside cardiovascular, pharmacogenomic, and other findings, in one purchase.^[1,12]

Whole-genome sequencing collects data across the full genome rather than a fixed gene list. For BRCA1 and BRCA2, the practical question is which variant classes a given WGS service has validated for reporting: single-nucleotide changes, small insertions and deletions, and large structural rearrangements each require different analytical pipelines. Ask what your report's BRCA analysis specifically covers.^[12]

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HLI's whole-genome service assesses BRCA1 and BRCA2 as part of a broader cancer-risk analysis. A genetics professional can help determine the right test and interpret results in the context of personal and family history.