GPNMB and glioblastoma: GPNMB is a type I transmembrane protein abundantly expressed in melanoma compared to normal tissue and other solid tumors such as glioblastoma and breast cancer where it has been reported as a prognostic factor (Kuan et al, 2006; Maric et al, 2013; Huang et al, 2021b; Feng et al, 2020).