IGF1 and obesity due to melanocortin 4 receptor deficiency: The consistent finding that obesity is a risk factor for human renal cell cancer, and the knowledge that obesity may lead to a hyperestrogenic environment and increased levels of insulin and insulin-like growth factor (IGF-1) (Azziz, 1989; Frystyk et al, 1995), provides indirect support that hormonal factors may play a role in human renal carcinogenesis.