Genomic Characterization of Aggressive Breast Cancer in Younger Women

Purpose: Although breast cancer (BC) risk increases with age, BC in younger women is more aggressive with higher mortality compared with older women. We characterize the genomic landscape of BCs in younger women.

Methods: Clinicopathologic, molecular, and genomic differences across age groups (< 40 years, 40-60 years, > 60 years) in female BC patients were investigated in two large cohorts [AACR-GENIE8.1 (n = 11,594) and METABRIC (n = 2509)]. Cox-proportional regression analyzed the prognostic impact of age groups for disease-specific survival (DSS) and recurrence-free survival (RFS) in METABRIC and progression-free survival (PFS) in GENIE cohorts. Chi-squared test was used to assess statistical associations between genomic alterations and age groups.

Results: Survival analysis showed that women < 40 years had shorter DSS [hazard ratio (HR): 1.52, p = 0.005], RFS (HR: 1.4, p = 0.006), and PFS (HR: 1.82, p = 0.0003) compared with women 40-60 years, and shorter RFS (HR: 1.5, p = 0.001) and PFS (HR: 2.95, p < 0.0001) compared with women > 60 years. Molecular subtypes in the METABRIC cohort showed women < 40 years were enriched with basal, and HER2+ subtypes, and less enriched with luminal A and B subtype (p < 0.0001). Characterization of genomic alterations in both cohorts demonstrated that BCs in women < 40 years were more enriched with TP53 mutations (FDR < 0.0001), BRCA1 mutations (FDR = 0.01), ERBB2 amplifications (FDR < 0.001), CDK12 amplifications (FDR < 0.001), and PPM1D amplifications (FDR < 0.001). In contrast, BCs in older women (> 60 years) were more enriched with PIK3CA, KMT2C, and CDH1 mutations (FDR < 0.0001).

Conclusions: BCs in young women are associated with shorter survival and more aggressive genomic features, including mutations in TP53 and BRCA1, and amplifications in ERBB2 and CDK12. These findings have the potential to impact clinical trial design and treatment.