Argonaut-2 (Ago2), the catalytic subunit of the RISC complex that mediates miRNA-dependent cleavage/degradation in mammals [154, 170, 214], expression is higher in ERα-negative, HER2-positive (basal) than ERα-positive/HER2 negative (luminal) human breast cancer cell lines and tumors [14]. The gene discussed is ESR1; the disease is breast cancer.