Direct activation of β-adrenoceptor signalling elevated COX2 expression and PGE2 production in primary bone marrow-derived macrophages (Fig. 5f,g) and human monocyte-derived macrophages (Supplementary Fig. 5E), while physiological activation of β-adrenoceptor signalling by chronic stress elevated COX2 expression in CD11b+F4/80+ macrophages isolated from primary mammary tumours (Fig. 5h). Here, PTGS2 is linked to breast cancer.