Epidemiological studies that have examined the relationship between prolactin levels and all-cause cancer and/or breast cancer reported inconsistent results (Tworoger et al. 2006, 2013, Dekkers et al. 2010, 2015, Berinder et al. 2011, Tikk et al. 2015, Wang et al. 2016, Soto-Pedre et al. 2017, Pekic et al. 2019a). Here, PRL is linked to breast cancer.