ERBB2 and cancer: We found that the 3’UTR of ERBB2 in only ERBB2-expressing cancer cells MCF7, BT474, and T47D (Supplementary Figures S3A, B, C, and E) is enriched with UUUUUU sequences which are mRNA-stabilizing elements (Figure 1A; Supplementary Figures S3A, B, C, E; Supplementary Figures S4A).