Of these, 172 papers met the inclusion criteria and were taken forward for data extraction (Fig. 1): 31 papers (representing 31 independent studies) examining the milk–IGF relationship; 132 papers (representing 125 studies) examining the IGF–prostate cancer relationship in humans; and ten papers (representing ten studies) examining the IGF–prostate cancer relationship in animals. Here, IGF1 is linked to Familial prostate cancer.