Three small case–control studies have examined circulating IGF‐I concentrations and risk of melanoma, but the findings were inconsistent.10, 11, 12 The reason for the inconsistency in the results of these case–control studies is unclear, but the selection of controls in a case–control study can bias the association between exposure and disease.13 In addition, the results of case–control studies may be influenced by reverse causation bias if the presence of disease affects circulating IGF‐I concentrations. The gene discussed is IGF1; the disease is melanoma.