POSTN and breast cancer: Stable microvasculature constitutes a dormant niche for DTCs.62 Thrombospondin‐1 (TSP‐1) secretion by mature endothelial cells induces the sustained quiescence of breast cancer cells, whereas sprouting microvasculature secretes TGF‐β1 and periostin (POSTN) to promote tumour growth,62 indicating that the dormancy and re‐activation of DTCs are closely associated with the vascular basement membrane.