For a patient being considered for olaparib therapy, which specimen should be used for BRCA1/2 testing: a blood sample for germline analysis or a tumor tissue sample for somatic analysis?

BRCA1/2 Testing Specimen Selection for Olaparib Therapy

For patients being considered for olaparib therapy, you should perform germline BRCA1/2 testing on blood samples first for all patients with epithelial ovarian cancer, followed by somatic tumor tissue testing only in those without a germline mutation. 1

Testing Algorithm

The ASCO 2020 guideline establishes a clear two-step approach 1:

1. First: Germline testing on blood - All women with epithelial ovarian cancer should undergo germline BRCA1/2 testing
2. Second: Tumor tissue testing - Only patients without a germline pathogenic variant should proceed to somatic tumor testing

This sequential strategy is recommended because:

• Germline mutations account for the majority of BRCA pathogenic variants in ovarian cancer
• Blood testing is technically simpler, more reliable, and has lower failure rates
• Identifies hereditary risk for family members
• Tumor testing adds only 3-9% additional somatic mutations beyond germline carriers 2

Specimen Options and Performance

Blood Samples (Germline Testing)

• Primary specimen choice for initial testing
• Technically straightforward with high success rates
• Detects germline BRCA1/2 mutations (the majority of cases)
• Can identify large genomic rearrangements that tumor testing may miss 3

Tumor Tissue (Somatic Testing)

• Use formalin-fixed, paraffin-embedded (FFPE) tumor blocks when germline testing is negative
• Identifies somatic BRCA mutations (6.4% of cases not detected by germline testing) 3
• Acceptable turnaround time of approximately 37 days median 3
• Low failure rate of only 4.4% 3
• Can be performed via next-generation sequencing using either hybrid capture or amplicon-based methods

Alternative: Malignant Ascites

• Cytological specimens from ascites are a valid alternative when tumor tissue is unavailable or insufficient 4
• Shows 100% concordance with FFPE tissue results for both germline and somatic variants 4
• Less invasive option, particularly useful at initial diagnosis when ascites is present
• Feasible even with low tumor fraction

Clinical Context for Olaparib Benefit

The magnitude of benefit from olaparib varies significantly by mutation status 1:

• BRCA-mutated tumors (germline or somatic): Hazard ratio 0.18-0.31 for progression-free survival
• HRD-positive/BRCA wild-type: Hazard ratio 0.43-0.50
• HRD-negative: Hazard ratio 0.68-0.92

BRCA2 mutations show particularly exceptional benefit compared to BRCA1, with some studies showing hazard ratios as low as 0.12-0.20 for BRCA2 carriers 1, 5.

Important Caveats

• While tumor-first testing strategies may be more cost-effective 6, the ASCO guideline prioritizes germline-first testing to ensure family members can benefit from cascade testing
• Olaparib is FDA-approved for both germline and somatic BRCA mutations in multiple settings (first-line maintenance, recurrent disease) 1
• Testing should not delay treatment initiation—results can guide maintenance therapy decisions after initial chemotherapy response
• The 3-9% of patients with somatic-only mutations would be missed without tumor testing, representing a meaningful population who can benefit from PARP inhibitor therapy 3, 7