PECAM1 and colorectal carcinoma: On the other hand, although the frequency of CD133+HIF-1α+ (i.e. hypoxic CSCs) was also elevated in CRC specimens with advanced stage CRC (Fig. S1c, and Fig. 1e), the CD133+HIF-1α+ cells were generally located far away from the CD31+ cells, suggesting that hypoxic CSCs have limited access to circulation and cannot easily form distant metastatic lesions (Fig. S1b and Fig. 1e).