BRCA1/2 mutation carriers vs the general breast cancer population (N = 799,986): 21-gene assay-based molecular characterization

Purpose: We compared 21-gene recurrence score (RS) distribution and expression of the single-gene/gene groups within this assay between BC patients with pathogenic variants (PV) in BRCA1/2 vs the general 21-gene-tested BC population. Methods: This retrospective study included consecutive 21-gene-tested female ER + HER2-negative BC patients with germline PVs in BRCA1/2. RS/gene expression data were compared to a previously described commercial use database (CDB, N = 799,986). Chi-square and 1-sample t test were used to compare RS distribution and single-gene/gene group scores between the study group and the CDB. Results: Study group patients (N = 81) were younger and their RS results were higher compared to the CDB (age: median [IQR], 56 [47–61.5] vs 60 [51–67] years; p < 0.001; proportion of patients with RS ≥ 26: 49.4% vs 16.4%, p < 0.001). Expression of 12/16 cancer genes in the assay and the ER, proliferation, and invasion gene group scores differed significantly between the study group and the CDB, all in a direction contributing to higher RS. The differences between the study group and the CDB were mostly retained, upon stratifying the patients by menopausal status. Conclusion: BC patients with PVs in BRCA1/2 have higher RS results that stem from distinct gene expression profiles in the majority of genes in the 21-gene assay.