In the present study we have shown that estrogenic GPER signalling triggers a feedforward loop which couples IL1β induction by CAFs to IL1R1 expression by cancer cells, toward the up-regulation of IL1β/IL1R1 target genes like PTGES, COX2, RAGE and ABCG2 and invasive features of breast cancer cells such as fibroblastoid cytoarchitecture and F-actin reorganization (see the schematic representation in Fig. 9). Here, GPER1 is linked to cancer.