IGF1 and colorectal cancer: This hypothesis is further supported by the findings that elevated circulating levels of C-peptide and IGF-I are associated with an increased risk of colorectal cancer (Kaaks et al, 2000; Sandhu et al, 2002; Ma et al, 2004; Renehan et al, 2004; Schoen et al, 2005; Jenab et al, 2007; Otani et al, 2007).