Targetable genomic mutations in young women with advanced breast cancer.

Abstract

1027 Background: Advanced breast cancer in women < 40 years is more aggressive, with worse prognosis and disease-free survival, compared to older women with the disease. With increasing availability of targeted and immune therapies, we aimed to compare genomic alterations (GA) using comprehensive genomic profiling (CGP) of tumor tissue. Methods: We analyzed 2,049 breast cancers submitted to Foundation Medicine for CGP. Hybrid-capture based CGP was performed to evaluate all classes of GA. Tumor mutational burden (TMB) was determined on at least 0.8 Mbp of sequenced DNA and microsatellite instability was determined on at least 95 loci. Tumor cell PD-L1 expression (defined as tumor proportion score >/= 1) was determined by IHC (Dako 22C3). We identified 28 (1.37%) patients <30 years, 159 (7.76%) between 30-39 years, and 1862 (90.87%) >/= 40 years. Breast tissue was used for CGP in 69.5% of cases and remainder of specimens were lymph node, metastatic, or unspecified. Results: Breast tumors were less likely to be estrogen receptor positive in younger women (54% of those <30 years, 60% of those 30-39 years, 69.4% of those >/= 40 years) and more likely to be triple negative (43%, 33%, 26.1% in the same respective groups). There was no clear pattern in HER2+ status by age (0%, 15.1%, 7.2%). Younger women had higher rates of BRCA1 (17.9%, 10.1%, 2.6%), BRCA2 mutations (7.10%, 5.70%, 4.1%), and RB1 mutations (14.3%, 9.4%, 6.1%), and lower rates of CDH1 (7.1%, 5%, 15.4%) and PIK3CA mutations (17.9%, 17.6%, 40.0%). Younger women were more likely to have PD-L1 expression (55.6%, 54.4%, 51.5%) but had lower frequencies of TMB >10 (0.0%, 5.0%, 8.7%). Differences are statistically significant in BRCA1, CDH1, and PIK3CA. Conclusions: These findings confirm that young women with breast cancer have actionable GA. Different mutational profiles may support differential use of targeted and immune therapies. Statistically and clinically significant differences include higher BRCA1 mutations which may lend to PARP inhibitor use and lower PIK3CA mutations which may reduce alpelisib use. Higher RB1 mutations and immunotherapy biomarker differences were not statistically significant. However, these may clinically translate into CDK4/6 resistance and reduced immunotherapy options, respectively. [Table: see text]