CCL2 and obesity due to melanocortin 4 receptor deficiency: Macrophages are recruited and activated by monocyte chemoattractant protein 1 (MCP1, also known as CCL2), secreted by adipocytes during obesity, and are necessary for tumour progression (Arendt et al, 2013); accordingly, loss of MCP1 delays mammary tumourigenesis in a triple‐negative breast cancer model (Cranford et al, 2017).