Prognostic value of structural variants in early breast cancer patients

Abstract

Genomic analysis of structural variants(SVs) in breast cancer (BC) patients has been conducted, but the relationship between genomic alterations and BC prognosis remains unclear. We performed RNA sequencing of 297 early BC fresh-frozen tissues. We identified SVs using three tools (STAR.Arriba, STAR.fusion, and STAR.SEQR) with the COSMIC and Mitelman databases as guide references. We found a median of five to eight fusions per sample. In BC intrinsic subtypes, normal subtype had the fewest fusions (median: 1, interquartile range [IQR]: 0, 3) followed by luminal A (median: 5.5, IQR: 2.75, 10.25), luminal B (median: 9, IQR: 6, 16.5), HER2-enriched (median: 9, IQR: 6, 16.5) and basal (median 10, IQR: 6, 15.5) subtypes (p < 0.05). Intrachromosomal fusion was more frequent observed rather than interchromosomal fusion. In location, chromosome 17 had the most fusions followed by chromosome 1 and 11. When samples were divided into high and low fusion groups based on a cut-off value of 11 fusions, five-year event-free survival (5Y-EFS) was 68.1% in the high fusion group (n = 72) and 80.1% in the low fusion group (n = 125) (p = 0.024) while 75.6% among all patients (95% confidence interval: 0.699, 0.819). Among BC subtype, TNBCs with more fusions had shorter EFS compared to those with fewer fusions (5Y-EFS rate: 65.1% vs. 85.7%; p = 0.013) but no EFS differences were observed in other BC subtypes. ESTIMATE ImmuneScore was also associated with the number of fusions in TNBC (p < 0.005) and TNBCs with high ImmuneScore had better 5Y-EFS compared to those with low ImmuneScore (p = 0.041). In conclusion, diverse fusions were observed by BC subtype, and the number of fusions was associated with BC survival outcome and immune status in TNBC.