By comparing the expression differences and correlations of PTN, MDK, and MIF, three ligand molecules that are more active in IBC tumour cells, we found that expression levels of PTN molecules were significantly upregulated in IBC tumour cells and that there was a significant positive correlation between the pathway scores of these three ligand molecules and the HER2 signature gene set scores (Extended Data Fig. S8a). This evidence concerns the gene MDK and neoplasm.