CD9 and neoplasm: CD9 gene expression within metastatic primary lung tumours (pT × N1and pT × N2) and secondary lung metastasis (M) showed a direct correlation between the downregulation of CD9 expression and the metastatic status of hLT; 70, 30, and 22.2% of pT × N1, pT × N2, and M, respectively, expressed CD9 more in tumour cores than in their surrounding tissues (Figure 2C).