Thirdly, because no included study did distinguish between type 1 and 2 DM (3 studies investigated the association between PCa risk and insulin use among patients with type 1 and 2 DM together, and the other 7 studies only investigated the association between PCa risk and insulin use among patients with type 2 DM, seen in table 1), we haven't done sub-group analysis according to the type of DM. Here, INS is linked to diabetes mellitus.