BID and colorectal carcinoma: When CRC lines were xenografted into CD1 nude mice, a striking reciprocal relationship was observed between the hypoxia marker pimonidazole, which formed a penumbra adjacent to necrotic regions in tumours (a location typically associated with chronic hypoxia), and Bid expression, which stained more positively away from the necrotic regions (Erler et al, 2004).