In agreement with this, we noticed—with two exceptions (Calu-3 for blood vessels and E35CR for macrophages)—that the staining density of CD31 and F4/80 was always higher in PDX models (Fig. 4d–g), corroborating the positive correlation between these two biomarker features and tumour-targeted drug delivery. This evidence concerns the gene PECAM1 and neoplasm.