Recent findings with the folate receptor alpha (FRα)-targeting ADC IMGN853 (mirvetuximab soravtansine) in patients with platinum-resistant epithelial ovarian cancer and with the delta-like protein 3 (DLL3)-targeted ADC SC16LD6.5 (rovalpituzumab tesirine) in patients with recurrent/refractory small-cell lung cancer indicate that expression levels of the target tumor-associated antigens may represent useful biomarkers for patient selection in ADC-based therapy [24, 25]. The gene discussed is DLL3; the disease is ovarian carcinoma.