TMPRSS4 and lung cancer: LSR may also activate the SARS−CoV−2 S proteins and increase the viral infection of lung cancer cells (Gong et al., 2023), along with host co-receptors that might be involved in cell infection, such as NETO2, GRP87, and transmembrane protease serine 4 (TMPRSS4) (Avdonin et al., 2023) (Figure 6).