CSPG4 and melanoma: Despite abundant CSPG4 cell surface expression, in vitro cytotoxicity assays demonstrated that all GBM xenografts, all breast cancer cell lines, and the DM443 melanoma cell line were highly resistant to both Mel-14-PE38KDEL and 9.2.27-PE38KDEL ITs (IC50 >100 ng/ml) (Tables 1 and 2).