IGF1 and benign prostatic hyperplasia: One in vitro study suggested that metformin may repress the growth of benign prostatic epithelial cells by inhibiting insulin‐like growth factor 1 (IGF‐1) and IGF‐1 receptor (IGF‐1R) secretion in stromal cells.5 However, population‐based study of metformin efficacy on BPH was limited because it is difficult to perform a randomized population trial.