The RQ assay was specifically able to detect HER2 gene amplification, as the reference gene chosen (CNTNAP1) lies on the same chromosome as HER2. There is clearly potential for changes in copy number in tumour DNA, and hence it would be preferable to use a panel of reference genes to detect amplification, but limiting cfDNA quantities prevent using such an approach. This evidence concerns the gene CNTNAP1 and neoplasm.