GPNMB and cancer: Subsequent studies revealed that GPNMB is expressed not only in cancer cells but also in many normal cells including macrophage, dendritic cell, osteoblast, microglia, and neuron, and it has been associated with various pathological conditions such as colitis, nonalcoholic steatohepatitis, amyotrophic lateral sclerosis, glaucoma, and neuroinflammation in addition to cancer progression, while its causal relevance in these diseases remains unclear (8, 9, 10).