ERBB2 and neoplasm: For example, a ctDNA-based signature tracking RB-LOH gene expression signature16, which is enriched in E2F target genes and tracks tumor proliferation rates (Supplementary Fig. 4), was found positively correlated to the PAM50 RNA-based Basal-like, HER2-enriched and proliferation tumor signatures, and negatively correlated to the PAM50 RNA-based Luminal A tumor signature (Fig. 2e).