(A) Venn diagram showing overlapping Ewing sarcoma cell-surface markers identified from 3 independent datasets: the Human Protein Atlas (blue), Ewing sarcoma–focused surface proteomics (red), and curated EWS:FLI1 target genes (green). (B) DepMap waterfall plot demonstrating cell viability changes following CRISPR-mediated LINGO1 depletion. (C) FACS analysis of cell-surface LINGO1 expression in indicated Ewing sarcoma cells. (D) Immunoblot for apoptosis markers in MHH-ES-1 cells 3 days after opicinumab-SN38 treatment. (E and F) Tumor volumes and weights of MHH-ES-1 xenografts (n = 10) treated with indicated agents. Arrows indicate treatments. (G) Body weights of mice from E and F. n = 5. (H) MMAE biodistribution 7 days after opicinumab-MMAE treatment. n = 5. (I and J) Tumor volumes and weights of TC-32 xenografts treated with indicated agents. n = 10 (vehicle), 8 (MMAE and opicinumab-MMAE), and 9 (irinotecan). (K and L) Serum concentrations of opicinumab and opicinumab-MMAE in opicinumab-MMAE–treated mice. n = 4. (M) Alanine aminotransferase (ALT) activity on day 17 in mice from I and J. n = 4. (N) Mouse body weights from I and J. n = 5 (vehicle/irinotecan) and 4 (MMAE/opicinumab-MMAE). Data represent mean ± SEM. P values were calculated using 2-way ANOVA with Bonferroni’s test (E) or Tukey’s test (I and N), unpaired 2-tailed Mann-Whitney test (F), 1-way ANOVA with Dunnett’s test (H), and Kruskal-Wallis with Dunn’s test (J and M).