Beyond BRCA in Breast Cancer: Olaparib for Germline PALB2 and Somatic BRCA Mutations
In this article
Olaparib was found to be effective not only in people with inherited BRCA mutations, but also in those with a PALB2 mutation and in patients whose tumors acquired a BRCA mutation.
- gPALB2: An inherited mutation often referred to as the "3rd BRCA."
- sBRCA (Somatic BRCA): BRCA mutations that are not present in a person's genes at birth, but develop later in the tumor tissue.
TBCRC 048 Expansion Cohort Results
The phase II TBCRC 048 study evaluated Olaparib treatment (300 mg, 2 times daily) by dividing 54 new patients with metastatic breast cancer (independent of the previous phase) into two main groups.
24 Patients
Patients with metastatic disease carrying an inherited PALB2 mutation.
30 Patients
Those without a BRCA mutation in their inherited genes, but with a BRCA1/2 mutation detected in their tumor.
Results: Who Benefits?
1. Those with a gPALB2 Mutation (Inherited)
The results in this group were, in a word, impressive. In patients with a PALB2 mutation, Olaparib showed effectiveness almost as high as in BRCA mutation carriers.
2. Those with an sBRCA Mutation (Somatic/Tumor-Derived)
Although responses in the somatic BRCA group were meaningful, they were not as high as in inherited mutation carriers. However, the notably long duration of effect (11.2 months) in patients who responded in this group was striking.
Detailed Comparison Table
| Parameter | gPALB2 (Inherited) | sBRCA (Somatic) |
|---|---|---|
| Median PFS (Progression-Free Survival) | 9.4 Months | 5.5 Months |
| Response Duration (Median) | 7.0 Months | 11.2 Months (Longer!) |
| Complete Response (CR) | 1 Patient | 2 Patients |
A Critical Detail: Biopsy or Liquid Biopsy?
A very important finding emerged in the study's somatic BRCA arm (Cohort 2a). The way the somatic mutation was detected played a critical role in predicting treatment success.
- Those Detected in Tumor Tissue: Response Rate %50 (18/36 patients)
- Those Detected by Liquid Biopsy (cfDNA in the Blood): Response Rate %10 (1/10 patients)
Comment: BRCA mutations detected only in the blood (cfDNA) may not be the tumor's main driver mutation (because of clonal hematopoiesis and other reasons). Therefore, tumor tissue analysis should remain the gold standard when making decisions about somatic BRCA.
This study once again strongly underlines the concept of "Personalized Oncology." In breast cancer, it is no longer enough simply to ask "Is there cancer in your family?" and look only at inherited BRCA tests.
Our Takeaways:
- PALB2 Should Become Routine: Patients with a PALB2 mutation benefit from PARP inhibitors as much as BRCA patients do. Failing to identify these patients means missing an opportunity for effective treatment.
- Tumor Genomics (NGS) Is Essential: Even if there is no mutation in the patient's blood (germline), there may be a BRCA mutation in the tumor itself (somatic). Olaparib is a meaningful option for this group too.
- The Source of the Test Matters: When looking for a somatic mutation, we should prefer tumor tissue if possible. Although liquid biopsy is practical, this study showed that tissue biopsy has greater predictive power.
In summary: Genetic mapping is no longer a luxury in metastatic breast cancer, but a necessity that changes treatment decisions.
References
- Tung NM, Robson ME, Li T, et al. TBCRC 048 (Olaparib Expanded) Expansion Cohorts: Phase II Study of Olaparib Monotherapy for Patients With Metastatic Breast Cancer With Germline Mutations in PALB2 or Somatic Mutations in BRCA1 or BRCA2. J Clin Oncol. 2026 Jan 28. DOI: 10.1200/JCO-25-02075.
- Tung NM, et al. TBCRC 048: Phase II Study of Olaparib for Metastatic Breast Cancer and Mutations in Homologous Recombination Repair (HRR) Genes. J Clin Oncol. 2020.
- NCCN Clinical Practice Guidelines in Oncology: Breast Cancer.
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