ERBB2 and breast cancer: It is worth noting that in advanced BC, a modestly superior OS (HR 0.95, 95% CI 0.91 to 0.99) was also observed by Frenel et al (n = 15,054) for HER2-low BC in a preliminary report [35], particularly for the hormone receptor-negative subgroup, although smaller studies have not detected significant differences [15–17].