SLC6A4 and neoplasm: Various other SLC6A4 polymorphic alleles with differential effects on tumor progression have been described in the literature (Chamba et al., 2010; Hallett et al., 2016; Ouyang et al., 2018; Phi van et al., 2015; Savas et al., 2012; Serafeim et al., 2002; Serafeim et al., 2003; Yoshimura et al., 2003; Zharinov et al., 2021).