ERBB2 and breast cancer: In contrast, knocking down hRNase 1 by small hairpin RNA (shRNA; sh-R1#1 and sh-R1#2) in KPL4 HER2+ breast cancer cells which express high levels of hRNase 1 (Supplementary Fig. 6a, b) significantly reduced the sphere-forming ability, the population of CD24−/CD44+ cells, and the TIC frequency (Fig. 2h–j and Supplementary Fig. 6c).