Indeed, we found that 4T1 cells co-injected with Il1b−/− fibroblasts expressed lower levels of Mmp1 and Mmp3 compared to cells co-injected with WT fibroblasts (Fig. 6g), suggesting that in addition to its effect on immune cell recruitment and on ECs, CAF-derived IL-1β enhances the invasiveness of breast cancer cells by upregulating their expression of MMPs. Here, MMP1 is linked to breast cancer.