PECAM1 and neoplasm: To investigate CSC abundance in normoxic compartments of the TME (i.e. normoxic CSCs), immunofluorescence was performed to assess the expression of CD133, a widely used CSC marker [17], in a variety of tumor specimens from patients with CRC co-stained with HIF-1α to denote hypoxic regions [18] and CD31 to denote blood vessels [19].