ADAM9 and central nervous system cancer: Given that other signaling pathways, such as extracellular signal-regulated kinase (Erk)1/2 activation, have been observed in HRH1 inhibition in BC cells [19] and shown to decrease ADAM9 expression in glioma cells [47], we cannot rule out the possibility that the ERK pathway may be involved in HRH1-mediated ADAM9 expression in OSCC cells, but this theory requires further investigation in the future.