Trastuzumab deruxtecan is a novel HER2-targeted ADC comprised of trastuzumab, a cleavable drug linker, and topoisomerase I payload (exatecan derivative) and has received accelerated approval by the FDA for the treatment of patients with HER2-positive, unresectable breast cancer who have received at least two prior lines of anti-HER2-based treatment protocols [46]. The gene discussed is ERBB2; the disease is breast cancer.