According to the relative expression levels of PSG9 in these cell lines and the tumorigenic and metastatic properties of these cell linesin vivo in light of subsequent mouse xenograft experiments, we stably expressed HA‐PSG9 in MDA‐231 cells and knocked down PSG9 in LM2‐4175 and Hs578T cells by infection with lentiviral vectors encoding HA‐PSG9 and shRNA targeting human PSG9 (shPSG9), respectively. The gene discussed is PSG9; the disease is infection.