IGF1 and obesity due to melanocortin 4 receptor deficiency: Our finding of an association between BMI and both colon and rectum cancers in men supports earlier observations (Lew and Garfinkel, 1979; Giovannucci et al, 1995; Pan et al, 2004; Samanic et al, 2004) and may be due to the growth-promoting effects of insulin and insulin-like growth factor (IGF-1), both increased in obesity (Calle and Kaaks, 2004).