Moreover, using an additional macrophage cell line (U937), we observed that the expression of selected ID4-dependent angiogenesis-related genes (EPHB2, GRN and NRP2) was induced in macrophages cultivated in CM compared with RPMI medium (Fig. 3c); as expected, this induction was impaired when CM was derived from si-ID4 BC cells (Fig. 3c–f). Here, NRP2 is linked to breast cancer.