Prospective Evidence Supports Tumor-First Multigene Testing in Ovarian Cancer

Multigene next-generation sequencing (NGS) performed directly on tumor tissue can accurately identify pathogenic variants in epithelial ovarian cancer (EOC), detecting both somatic and germline alterations with a false-negative rate of less than 1%, according to a prospective analysis from the Princess Margaret Cancer Centre in Toronto.¹

The findings, published in Molecular Oncology, support a tumor-first genetic testing model that could significantly reduce redundant testing and shorten the time to genetic counseling and eligibility for targeted therapy.

EOC remains the fifth leading cause of cancer-related death among women in North America.² Approximately 20% to 30% of cases are associated with inherited pathogenic variants in homologous recombination repair or mismatch repair genes, most commonly BRCA1 or BRCA2. Knowledge of BRCA1/2 status is central to therapeutic decision-making, particularly in identifying candidates for poly(ADP-ribose) polymerase inhibitor (PARPi) therapy, which has been shown to significantly prolong progression-free survival.³

Among the 106 tumor samples analyzed, 94.3% harbored at least 1 detectable variant.¹ Excluding the TP53 alterations typical in EOC, investigators identified 27 Tier I/II (clinically significant) variants and 58 Tier III variants of uncertain significance (VUS). Of the Tier I/II findings, 16 (59.3%) represented germline pathogenic or likely pathogenic variants, while 11 (40.7%) were somatic only. Overall, the tumor-first approach achieved 99.1% concordance with paired germline testing, correctly identifying both variant-positive and variant-negative cases in 105 of 106 patients.

In total, 28 clinically significant variants were identified across tumor and germline analyses, including BRCA1 (n = 17), BRCA2 (n = 6), RAD51C (n = 2), ATM (n = 1), PALB2 (n = 1), and PTEN (n = 1). Among germline pathogenic or likely pathogenic variants, BRCA1 accounted for 53%, followed by BRCA2 (29%), RAD51C (12%), and ATM (6%). For Tier I/II somatic variants, BRCA1 comprised 59%, BRCA2 22%, and RAD51C 7%.

Homologous recombination deficiency (HRD) testing was performed in 50 BRCA-negative tumors, of which 14 (28%) showed a positive genomic instability score (≥42). Two HRD-positive patients harbored clinically actionable variants: 1 germline RAD51C pathogenic variant and one tumor PALB2 Tier II variant, indicating that HRD analysis can expand the identification of patients responsive to PARPi beyond those with BRCA mutations alone. Conversely, 1 patient with a germline RAD51C variant was found to be HRD-negative (genomic instability score = 40), highlighting the need for complementary approaches in comprehensive treatment stratification.

Nearly half of all patients (51 of 106; 48%) exhibited no tumor variants beyond TP53, and 50 of these 51 (98%) also tested negative on paired germline analysis. This high concordance suggests that tumor-first multigene screening could safely eliminate the need for separate germline assays in roughly half of patients with EOC.

Clinically, these findings validate tumor-based NGS panels as an effective tool for triaging genetic testing in the frontline setting. When no clinically relevant variants are detected, excluding TP53, the likelihood of a missed germline pathogenic variant appears exceedingly low, supporting a selective rather than universal approach to follow-up germline testing. Such testing may be reserved for patients with a compelling family history, early-onset disease, or features suggestive of hereditary syndromes, such as Li-Fraumeni syndrome.

Implementing a tumor-first workflow could streamline genetic evaluation, reduce turnaround times, and conserve limited genetic resources by focusing counseling and confirmatory testing on those most likely to benefit.

“This model is expected to decrease workloads for both molecular genetics laboratories and hereditary cancer clinics," the authors wrote. "This is important given that wait times for genetics assessments are a recognized barrier to accessing genetic testing in Canada and across North America.”

References

1. Spenard E, Mitric C, Care M, et al. Tumor and germline testing with next-generation sequencing in epithelial ovarian cancer: a prospective paired comparison using an 18-gene panel. Mol Oncol. 2025;19(10):2157-2171. doi:10.1002/1878-0261.70136
2. Siegel RL, Giaquinto AN, Jemal A. Cancer statistics, 2024. CA Cancer J Clin. 2024;74(1):12-49. doi:10.3322/caac.21820
3. Zhou Y, Xu J. Impact of PARP inhibitors on progression-free survival in platinum-sensitive recurrent epithelial ovarian cancer: a retrospective analysis. World J Surg Oncol. 2024;22(1):276. doi:10.1186/s12957-024-03562-8