CTSK and neoplasm: Similarly to the other tumours generated in this study, these allograft tumours stained positively for PMEL, CATHEPSIN K, PDGFRβ, SMA and VIMENTIN (Supplementary Fig. 10e), expressed PMEL by western blotting (Supplementary Fig. 10f), and exhibited a similar frequency of PMEL expressing cells (Supplementary Fig. 10g).