FLT1 and rheumatoid arthritis: There is strong evidence that PlGF and VEGFR1 signaling can influence how immune cells affect tumor growth and metastasis (Albonici et al., 2019; Ceci et al., 2020; Incio et al., 2016; Kim et al., 2012; Muramatsu et al., 2010; Qian et al., 2015) as well as cardiovascular disorders (Luttun et al., 2002; Raisky et al., 2007; Roncal et al., 2010) or rheumatoid arthritis (Murakami et al., 2006).