Some authors use the relative number of HER2 + stained tumor cells, but thresholds vary from < 30% (van Cutsem et al. 2015), < 40% (Haffner et al. 2021), to < 60% (Kanayama et al. 2018; Wang et al. 2014) or even < 100% tumor cells stained HER2-positive (Wakatsuki et al. 2018; Yagi et al. 2019). The gene discussed is ERBB2; the disease is neoplasm.