CYP27B1 and rectal cancer: Subsite-related differences in CYP27B1 expression were apparent to some extent in low-grade (G1 and G2) cancerous lesions as rectal cancers expressed almost twice as much CYP27B1 than tumors located in the proximal (p < 0.05) and distal colon (p < 0.01) (Figure 3).