ESR1 and neoplasm: In this analysis, we identified other interesting DE circRNAs including Circ_HIPK3_3, which was highly expressed in all tumor samples analyzed; Circ_GFRA1_5-7, which was significantly overexpressed in ER+ tumors only; and Circ_RPPH1_1 as an extremely abundant circRNA in HER2+ tumors (Figure 4C).