Efficacy of ABBV-321 in suppressing tumor growth was evaluated in PDX #1174, a malignant mesothelioma PDX tumor model (EGFR IHC score of 3+). Significant tumor growth suppression was demonstrated with ABBV-321 dosed at 0.15 mg/kg 2 every seven days ×3 compared to groups treated with either non-targeted ADC or cisplatin (Fig. 3G). These results suggest a novel therapeutic approach for treatment of malignant mesothelioma with EGFR overexpression.