BRCA1/2 Testing in Ovarian Cancer: What a Pathogenic Variant Determines

A germline BRCA1 result lands in the chart a few weeks after a woman with high-grade serous ovarian cancer has finished her first platinum-based course. That single line — pathogenic variant present — reshapes the conversation about maintenance therapy, and it sends ripples outward to her sisters and daughters. This is one of the highest-yield tests in gynecologic oncology, and understanding what it does and doesn't tell us is worth the effort.

What the Test Measures

BRCA1 and BRCA2 encode proteins central to homologous recombination repair (HRR), the high-fidelity system that mends double-strand DNA breaks. When both functional copies of either gene are lost in a tumor cell, that repair pathway fails. The cell falls back on error-prone alternatives and accumulates damage.

That failure is exactly what makes these tumors vulnerable. PARP enzymes handle single-strand break repair; inhibit PARP in a cell that already can't perform homologous recombination, and unrepaired lesions convert into lethal double-strand breaks. The tumor cell dies while normal cells, with intact BRCA function, survive. This is synthetic lethality — two individually survivable defects that together are fatal.

The test detects a pathogenic (or likely pathogenic) BRCA1/2 alteration. It comes in two flavors. A germline variant is inherited and present in every cell, including blood. A somatic variant arises within the tumor alone. Functionally, at the level of the cancer cell, both produce the same defect in homologous recombination. That's why comprehensive testing looks for both.

How It's Tested

Two specimens, two questions.

Germline testing uses a blood (or occasionally saliva) sample and sequences constitutional DNA. Somatic testing uses formalin-fixed, paraffin-embedded (FFPE) tumor tissue analyzed by next-generation sequencing (NGS). Somatic NGS captures both somatic and many germline variants present in the tumor, but it won't reliably distinguish the two on its own — a variant found in tumor tissue may still warrant germline confirmation from blood.

Preanalytics matter more than people assume. FFPE is workable but imperfect: fixation fragments DNA and introduces sequencing artifacts, so adequate tumor cellularity and reasonable specimen quality are prerequisites. Both large rearrangements and small variants must be covered, because BRCA1/2 pathogenic alterations include point mutations, small insertions and deletions, and larger structural changes. An assay that misses copy-number events will miss real disease.

Scoring is deliberately binary at the reporting level: a pathogenic or likely pathogenic BRCA1/2 alteration is either present or absent. Variants of uncertain significance (VUS) are reported but do not qualify as a positive result.

What Each Result Means

BRCA-mutant. A pathogenic BRCA1/2 alteration is present — germline, somatic, or both. The tumor carries the homologous-recombination defect that underlies PARP-inhibitor sensitivity. A germline finding additionally carries implications for the patient's relatives.

BRCA wild-type. No pathogenic BRCA1/2 alteration was detected by the assay used. This is not the same as "no repair defect." Other HRR genes, or epigenetic silencing of BRCA1, can produce a similar phenotype that BRCA sequencing alone won't see.

Here's a practical caveat. Wild-type means "not found by this test," not "definitively absent."

What It Determines for Treatment Eligibility

The predictive value is the point. A pathogenic BRCA1/2 alteration informs eligibility for PARP-inhibitor therapy — both as maintenance and as treatment — in high-grade serous and other epithelial ovarian cancers.

The evidence base rests on randomized companion-diagnostic-linked trials. In newly diagnosed advanced disease with a BRCA mutation, maintenance olaparib after platinum-based chemotherapy substantially prolonged progression-free survival [1]. Broader guideline synthesis has since positioned PARP inhibitors within the ovarian cancer management pathway according to biomarker status [2].

Two things belong to the treating oncologist, not the pathologist. Whether a given patient receives a PARP inhibitor. And which agent, at what point in the disease course. The biomarker establishes eligibility for a drug class; it does not prescribe.

A germline result also carries consequences beyond this patient. It informs risk-reducing surgical discussions and enables cascade testing — the systematic offer of testing to at-risk blood relatives. One tumor result can protect an entire family.

Caveats and What's Evolving

The most important limitation is conceptual: BRCA1/2 is a narrow window onto a wider biological state called homologous recombination deficiency (HRD). Tumors can be HR-deficient without a BRCA mutation — through alterations in other HRR genes or through BRCA1 promoter methylation.

This is where HRD assays enter. Rather than reading a single gene, they quantify the consequences of defective repair — the genomic scars left behind. These scores typically integrate metrics such as loss of heterozygosity (LOH), telomeric allelic imbalance, and large-scale transitions, sometimes combined with BRCA status itself. The logic is elegant: a cell that couldn't repair breaks properly leaves a characteristic pattern of damage across its genome, and that pattern persists even after the causal defect is gone.

So why hasn't HRD simply replaced BRCA? Because BRCA remains the cleaner, more reproducible biomarker. A pathogenic BRCA variant is a discrete, verifiable molecular event with a mechanistic through-line to PARP sensitivity. HRD scores rely on assay-specific thresholds that are still being refined, and the cutoffs distinguishing "deficient" from "proficient" are contested and platform-dependent. HRD casts a wider net; BRCA offers a firmer footing. In practice, the two are used together — BRCA as the anchor, HRD to extend eligibility considerations to a broader population.

Two further points. VUS reclassification means today's uncertain variant may become tomorrow's pathogenic call, so periodic re-review is worthwhile. And assay sensitivity varies — a wild-type result reflects the method used, and a negative germline test doesn't exclude a somatic event, or vice versa.

The takeaway I'd leave with any reader is this. BRCA is the sharpest single predictive marker we have in this disease, and it remains the reference point around which the expanding HRD landscape is organized. As assays broaden, they don't retire BRCA — they build outward from it.

References

1. Moore K, Colombo N, Scambia G, et al. Maintenance Olaparib in Patients with Newly Diagnosed Advanced Ovarian Cancer. N Engl J Med. 2018;379(26):2495–2505.
2. Armstrong DK, et al. PARP Inhibitors in the Management of Ovarian Cancer: ASCO Guideline. J Clin Oncol. 2022. PMCID: PMC8942301.