“…From these studies only two did not report the clinical characteristics of the control groups (Maegdefessel et al 2012a(Maegdefessel et al , 2012b) and in Maegdefessel et al (2014), even though the clinical characteristics were reported for control plasma samples, they were not reported for control tissue samples. In addition, cases and control groups were age and gender matched in 16 studies (Boon et al 2011, Jones et al 2011, Liao et al 2011, Kin et al 2012, Pahl et al 2012, Patuzzo et al 2012, Biros et al 2014, Ikonomidis et al 2013, Zampetaki et al 2014, Chan et al 2015, Pei et al 2015, Wang et al 2015, Zhang et al 2015, Busch et al 2016, Licholai et al 2016, Wu et al 2016. For three studies we could not determine whether the gender of cases and control groups for tissue samples match since the gender was not clearly stated for the control groups (Maegdefessel et al 2012a(Maegdefessel et al , 2012b(Maegdefessel et al , 2014.…”