Patients experienced neutropenia, skin rash and mucosal inflammation as dose limiting toxicities, indicating the broad Trop-2 expression in normal epithelia (Stepan et al., 2011; Trerotola et al., 2013a; Trerotola et al., 2021) as a key hurdle in Trop-2-targeted therapy, and showing distinct primate toxicity as a pivotal indicator for human studies. The gene discussed is TACSTD2; the disease is neutropenia.