ACE2 and COVID-19: Another study using TCGA reported increased expression of ACE2 and TMPRSS2 in lung and oral cancer tissues from smokers which may indicate increased susceptibility of smokers to COVID-19 because of the increased expression of binding receptors for SARS-CoV-2, however there is not enough data from immunohistochemistry on patient tissues (Chakladar et al., 2020).