It has been reported for ERBB2, another therapeutic target of ADC-based therapies, that higher intra-tumoral heterogeneity found by ERBB2-FISH in ERBB2-positive breast cancer patients treated by an anti-ERBB2 therapy, correlated with worse outcome compared to those without ERBB2 heterogeneity [20]. The gene discussed is ERBB2; the disease is breast cancer.