Residency · Residency · Medical Genetics Genomics
Hereditary Breast and Ovarian Cancer: BRCA1/2 and Beyond
BRCA1 and BRCA2
Gene Functions
BRCA1, located at 17q21, is a tumor suppressor involved in homologous recombination repair (HRR) of double-strand DNA breaks, cell cycle checkpoint control, transcription regulation, and chromatin remodeling. BRCA2, at 13q13, is essential for RAD51-mediated homologous recombination and functions by loading RAD51 onto single-stranded DNA at sites of double-strand breaks. Loss of function of either gene leads to impaired DNA repair, genomic instability, and cancer predisposition following the Knudson two-hit model.
Cancer Risks
BRCA1 carriers face a lifetime breast cancer risk of 55 to 72% and an ovarian cancer risk of 39 to 44%, with additional elevated risks for pancreatic cancer, prostate cancer (modestly), and contralateral breast cancer. BRCA2 carriers have a lifetime breast cancer risk of 45 to 69% and an ovarian cancer risk of 11 to 17%, along with elevated risks for pancreatic cancer (5 to 7%), prostate cancer (up to 20 to 30%), and male breast cancer (6 to 8%). These risks are modified by family history, the specific location of the variant within the gene (including the ovarian cancer cluster region in BRCA2), polygenic risk score, and reproductive factors.
Variant Spectrum
Over 2,000 pathogenic variants have been identified in each gene. Founder variants are particularly notable in the Ashkenazi Jewish population, where BRCA1 185delAG, BRCA1 5382insC, and BRCA2 6174delT occur at a combined carrier frequency of approximately 1 in 40. The Icelandic founder variant BRCA2 999del5 is another well-characterized example. Large genomic rearrangements account for approximately 10% of BRCA1 pathogenic variants but are less common in BRCA2. Biallelic BRCA2 mutations cause Fanconi anemia complementation group D1 (FA-D1), while biallelic BRCA1 mutations are typically embryonic lethal.
Moderate-Penetrance Genes
PALB2 (Partner and Localizer of BRCA2)
PALB2 confers autosomal dominant breast cancer predisposition with a lifetime risk of 33 to 58% depending on family history. Ovarian cancer risk is approximately 3 to 5%, and pancreatic cancer risk is also elevated. NCCN guidelines recommend enhanced breast screening with annual MRI plus mammography starting at age 30, and risk-reducing mastectomy should be discussed. Biallelic PALB2 mutations cause Fanconi anemia complementation group N.
ATM (Ataxia-Telangiectasia Mutated)
Heterozygous ATM carriers face a 2 to 3 fold increased breast cancer risk, translating to a lifetime risk of approximately 20 to 30%. There are moderate increases in ovarian and pancreatic cancer risk as well. NCCN recommends annual mammography plus breast MRI starting at age 40. Biallelic ATM mutations cause ataxia-telangiectasia. Notably, the specific missense variant c.7271T>G is associated with higher breast cancer risk than truncating variants.
CHEK2
The CHEK2 c.1100delC variant, the most extensively studied, confers a 2 to 3 fold increased breast cancer risk. There is a modest and debated increase in colon cancer risk, with no clear increase in ovarian cancer. NCCN recommends mammography plus breast MRI starting at age 40. CHEK2 has lower penetrance than BRCA1/2 or PALB2.
Other Genes on Multigene Panels
RAD51C and RAD51D primarily confer ovarian cancer predisposition with 5 to 10% lifetime risk and a modest breast cancer risk. BRIP1 carries an ovarian cancer risk of approximately 5 to 6%, with an uncertain breast cancer association. CDH1 predisposes to lobular breast cancer and diffuse gastric cancer as part of hereditary diffuse gastric cancer syndrome. PTEN mutations cause Cowden syndrome with a breast cancer risk of 25 to 50% alongside thyroid and endometrial cancer risks. STK11 mutations underlie Peutz-Jeghers syndrome, carrying a breast cancer risk of 32 to 54% along with gastrointestinal and gynecologic cancer risks.
| Gene | Penetrance | Lifetime Breast Cancer Risk | Lifetime Ovarian Cancer Risk | Other Cancer Risks | Breast Screening Recommendation |
|---|---|---|---|---|---|
| BRCA1 | High | 55–72% | 39–44% | Pancreatic, prostate | MRI + mammography from age 25–30 |
| BRCA2 | High | 45–69% | 11–17% | Pancreatic, prostate, male breast | MRI + mammography from age 25–30 |
| PALB2 | High (with FH) | 33–58% | 3–5% | Pancreatic | MRI + mammography from age 30 |
| ATM | Moderate | 20–30% | Modest increase | Pancreatic | MRI + mammography from age 40 |
| CHEK2 | Moderate | 20–30% (c.1100delC) | No clear increase | Colon (modest/debated) | MRI + mammography from age 40 |
| RAD51C/D | Moderate | Modest increase | 5–10% | — | Per NCCN guidelines |
| BRIP1 | Moderate | Uncertain | ~5–6% | — | Standard screening |
| CDH1 | High | Lobular breast 40–50% | — | Diffuse gastric cancer | MRI + mammography from age 30 |
| PTEN (Cowden) | High | 25–50% | — | Thyroid, endometrial | MRI + mammography from age 30 |
| STK11 (PJS) | High | 32–54% | Ovarian (sex cord) | GI, gynecologic | MRI + mammography from age 25 |
Risk Assessment Models
Family History-Based Models
The Tyrer-Cuzick (IBIS) model integrates family history, hormonal factors, breast density, and SNP-based PRS. BOADICEA/CanRisk is a Bayesian model that incorporates family history along with BRCA1/2, PALB2, CHEK2, and ATM variant status and PRS, and is endorsed by multiple guidelines. BRCAPRO is a Bayesian model focused on estimating BRCA1/2 carrier probability. Older models such as the Claus model and Gail model have narrower inputs and are less commonly used.
Testing Criteria
NCCN guidelines recommend genetic testing when personal or family history meets specific criteria. Testing is now recommended for all breast cancer patients at diagnosis regardless of age or family history in many guidelines. All patients with epithelial ovarian, fallopian tube, or primary peritoneal cancer should be tested regardless of family history. Population screening for BRCA1/2 is recommended in Ashkenazi Jewish individuals regardless of family history. Emerging evidence supports population-based BRCA screening more broadly, with studies such as the BRCA-P trial in progress.
Management of BRCA1/2 Carriers
Breast Cancer Risk Reduction and Surveillance
Enhanced screening consists of annual mammography plus breast MRI starting at age 25 to 30, with alternating modalities every 6 months for staggered screening. Risk-reducing bilateral mastectomy reduces breast cancer risk by approximately 90 to 95% and is discussed as an option rather than a requirement. Chemoprevention with tamoxifen or raloxifene reduces breast cancer risk by approximately 50%, primarily for estrogen receptor-positive tumors, though data specific to BRCA carriers are limited. Oophorectomy reduces breast cancer risk by approximately 50% in premenopausal BRCA1 carriers, with a less clear benefit in BRCA2 carriers.
Ovarian Cancer Risk Reduction
Risk-reducing bilateral salpingo-oophorectomy (RRSO) is recommended by age 35 to 40 for BRCA1 carriers and 40 to 45 for BRCA2 carriers, reducing ovarian cancer risk by approximately 80 to 90% and all-cause mortality. Salpingectomy with delayed oophorectomy is under investigation as an approach to preserve ovarian function longer while removing the fallopian tube, which is now recognized as the likely site of origin for high-grade serous carcinoma. There is currently no effective screening for ovarian cancer, as CA-125 and transvaginal ultrasound have insufficient sensitivity and specificity for this purpose.
Treatment Implications
PARP inhibitors (olaparib, niraparib, talazoparib) exploit synthetic lethality in HRR-deficient tumors and are approved for BRCA-associated breast, ovarian, pancreatic, and prostate cancers. BRCA-associated cancers are generally more sensitive to platinum-based chemotherapy. The OlympiA trial demonstrated that adjuvant olaparib reduces recurrence in HER2-negative, BRCA-mutated early breast cancer.
Multigene Panel Testing
Benefits
Multigene panels identify pathogenic variants in moderate-penetrance genes that would be missed by BRCA1/2-only testing. Actionable findings are found in approximately 4 to 5% of patients beyond BRCA1/2. Panel testing is cost-effective compared to sequential single-gene testing.
Controversies
A significant challenge is the high VUS rate: approximately 20 to 40% of patients receive at least one VUS, and this rate increases with the number of genes on the panel. Some genes on panels have limited clinical evidence or uncertain management guidelines. Gene content varies across commercial panels. Patient anxiety from VUS results is a real concern, underscoring the need for careful pre-test and post-test counseling about limitations.
Cascade Testing
All first-degree relatives of identified BRCA1/2 and PALB2 carriers should be offered testing. However, uptake remains suboptimal at approximately 30 to 50% of at-risk relatives. Barriers include family communication difficulties, insurance concerns, and psychological factors. Direct-to-family outreach programs and provider-mediated contact models are under study to improve uptake.
<image>A diagram showing the homologous recombination repair (HRR) pathway and the mechanism of PARP inhibitor synthetic lethality. Panel 1: Normal DNA repair showing a double-strand break being repaired by the HRR pathway with BRCA1 and BRCA2/RAD51 loading onto DNA. Panel 2: BRCA-deficient cell using error-prone repair (NHEJ) instead, leading to genomic instability and cancer. Panel 3: PARP inhibitor mechanism -- PARP enzyme normally repairs single-strand breaks; when PARP is inhibited, single-strand breaks convert to double-strand breaks during replication; BRCA-proficient cells repair these via HRR (survive), while BRCA-deficient cells cannot (synthetic lethality, cell death). The concept of synthetic lethality is labeled.</image>
<image>A comprehensive management timeline for a female BRCA1 carrier. Starting at age 18: breast self-awareness. Age 25: begin annual breast MRI. Age 30: add annual mammography (alternating with MRI every 6 months). Age 35-40: discuss and consider RRSO. A parallel timeline shows discussion points for risk-reducing mastectomy, chemoprevention options, and reproductive planning (fertility preservation before RRSO). Treatment boxes show PARP inhibitor eligibility if cancer develops. Family cascade testing arrows extend from the proband to first-degree relatives. Age-specific cancer risks are annotated along the timeline.</image>
<image>A gene penetrance comparison chart showing lifetime breast and ovarian cancer risks for BRCA1, BRCA2, PALB2, ATM, CHEK2, and RAD51C/D. Horizontal bar charts display breast cancer risk (blue bars) and ovarian cancer risk (red bars) for each gene, with the general population risk shown as a baseline reference line. Error bars indicate the range of published risk estimates. Management recommendations (screening modality and age to begin) are annotated next to each gene. A legend indicates high-penetrance (BRCA1/2), moderate-penetrance (PALB2, ATM, CHEK2), and lower-penetrance genes (RAD51C/D, BRIP1).</image>
Clinical Pearls
All patients with epithelial ovarian, fallopian tube, or primary peritoneal cancer should undergo BRCA1/2 testing (and ideally broader HRR gene testing) regardless of family history, as results directly impact treatment selection through PARP inhibitor eligibility and inform family management. PALB2 has been upgraded to a high-penetrance breast cancer gene in patients with significant family history, with lifetime risk approaching 50%, and management recommendations now parallel BRCA2 in many guidelines. The Ashkenazi Jewish BRCA1/2 founder variant carrier frequency is approximately 1 in 40, making population screening in this group cost-effective and recommended by multiple organizations. Risk-reducing salpingo-oophorectomy is the single most impactful intervention for BRCA1 carriers, reducing ovarian cancer risk by approximately 80 to 90% and all-cause mortality by about 70%, though timing should balance cancer risk reduction with quality-of-life considerations regarding premature menopause. PARP inhibitors exploit synthetic lethality in HRR-deficient tumors and represent one of the most successful examples of precision oncology, now approved across multiple BRCA-associated cancer types. A VUS on a multigene panel should not change clinical management; decisions should be guided by family history and other clinical factors until the variant is reclassified. Cascade testing remains critically underutilized, yet identifying one BRCA carrier can potentially save the lives of multiple relatives through early detection and prevention.
References
- Kuchenbaecker KB et al. Risks of breast, ovarian, and contralateral breast cancer for BRCA1 and BRCA2 mutation carriers. JAMA. 2017;317(23):2402-2416.
- NCCN Clinical Practice Guidelines: Genetic/Familial High-Risk Assessment: Breast, Ovarian, and Pancreatic. Version 2.2025.
- Robson M et al. Olaparib for metastatic breast cancer in patients with germline BRCA mutation. N Engl J Med. 2017;377(6):523-533.
- Yang X et al. Cancer risks associated with germline PALB2 pathogenic variants: an international study of 524 families. J Clin Oncol. 2020;38(7):674-685.
- Domchek SM et al. Association of risk-reducing surgery in BRCA1 or BRCA2 mutation carriers with cancer risk and mortality. JAMA. 2010;304(9):967-975.
- LaDuca H et al. Utilization of multigene panels in hereditary cancer predisposition testing. Genet Med. 2014;16(11):830-837.
