PTGS2 and squamous cell carcinoma: It has also been indicated in breast cancer in vivo that pre-irradiation of mice bearing breast cancer increased the number of circulating tumour cells (CTCs, often confirmed to be CSCs) and the incidence of lung metastasis via the elevated expression of cyclo-oxygenase-2 (COX2) and IL-6 in the TME.133 Similarly, in squamous cell carcinomas, it has been shown that CAF-secreted TGF-β induced by irradiation can promote the migration and invasion of cancer cells in vitro71 and increase the number of CTCs and lung metastasis in breast tumours in situ.134