Genetic Testing for Breast Cancer
All patients with breast cancer diagnosed at age ≤65 years should be offered BRCA1/2 testing at minimum, with multi-gene panel testing including high-penetrance genes (PALB2, TP53, PTEN, STK11, CDH1) offered based on personal and family history. 1
Who Should Be Tested
Newly Diagnosed Breast Cancer (Stage I-III or de novo Stage IV)
Age ≤65 years:
- Offer BRCA1/2 testing to ALL patients regardless of family history 1
- Multi-gene panel testing should be offered based on personal/family history 1
Age >65 years - Offer BRCA1/2 testing if ANY of the following:
- Candidate for PARP inhibitor therapy
- Triple-negative breast cancer
- Personal or family history suggesting pathogenic variant
- Assigned male sex at birth
- Ashkenazi Jewish ancestry or population with increased founder mutation prevalence 1
Recurrent or Metastatic Disease
- ALL patients who are PARP inhibitor candidates should receive BRCA1/2 testing regardless of age or family history 1
- This has the highest consensus agreement (97.5%) among all recommendations 1
- PALB2 pathogenic variants also show high response rates to PARP inhibitors 1
Second Primary Breast Cancer
- Offer BRCA1/2 testing for contralateral or ipsilateral second primary cancers 1
Prior Breast Cancer Without Active Disease
Age ≤65 at diagnosis:
- Offer BRCA1/2 testing if results will inform personal risk management or family assessment 1
Age >65 at diagnosis - Same criteria as newly diagnosed patients >65 1
Which Genes to Include
Core Panel - High-Penetrance Genes
The initial hereditary cancer panel should include:
- BRCA1/2 (mandatory baseline)
- PALB2 (informs PARP inhibitor therapy, surgical decisions, second cancer risk)
- TP53 (for patients diagnosed <40 years)
- PTEN
- STK11
- CDH1 1
These high-penetrance genes inform medical therapy, surgical decision-making, second primary cancer risk estimates, and family assessment 1.
Moderate-Penetrance Genes - Optional Addition
May be included (ATM, CHEK2, BARD1, RAD51C, RAD51D):
- Do NOT inform treatment of the index breast cancer
- May inform second primary cancer risk and family assessment
- Can be offered to patients undergoing BRCA1/2 testing 1
Important caveat: The 2025 ESMO guidelines recommend AGAINST including syndromic genes (STK11, PTEN, NF1, CDH1) in routine breast cancer panels due to insufficient evidence for improving cancer-related mortality, though the 2024 ASCO-SSO guidelines include them 2. The ESMO panel prioritizes only BRCA1, BRCA2, PALB2, RAD51C, RAD51D, and TP53 (for age <40) based on mortality impact 2.
Panel Selection Strategy
The specific multi-gene panel should be tailored to:
- Patient's personal cancer history
- Family history patterns
- Consultation with clinical cancer genetics provider when possible 1
Critical Implementation Points
Testing Timing
- Median time from biopsy to result can be reduced to 22 days with mainstream testing pathways 3
- Testing should occur early enough to inform surgical decisions
Common Pitfall: Age-Based Exclusion
- 42.3% of pathogenic variant carriers have NO family history of malignancy 4
- Nearly 8% of patients who don't meet NCCN criteria still have pathogenic variants 5
- Real-world data shows 10.8% positivity rate in patients ≥65 years 6
Post-Test Management
Pathogenic variants identified:
- Provide individualized genetic counseling
- Refer to clinical cancer genetics provider 1
Variants of uncertain significance (VUS):
- Should NOT alter management
- Require periodic follow-up for potential reclassification
- Occur in 47.5-55.8% of tested patients 1, 6
Negative results with significant family history:
- Still benefit from genetic counseling
- Recommend referral to clinical cancer genetics 1
Practical Consideration
Mainstream testing facilitated by breast care coordinators increases uptake from 31.7% to 61.6% and identifies more pathogenic variants (3.6% vs 1.6%) without increasing genetics consultation burden 3.