FOLH1 and prostate cancer: In the past, different PE-based immunotoxins against prostate cancer targeting the epidermal growth factor receptor family, interleukins, or the prostate specific membrane antigen (PSMA) were developed and tested preclinically (Debinski and Pastan, 1994; Maini et al., 1997; Kawakami et al., 2001; Husain et al., 2003; Baiz et al., 2013; Niesen et al., 2015; Meng et al., 2017; Fischer et al., 2020; Xing et al., 2021).