ESR1 and neoplasm: Furthermore, we also analyzed CIP2A in our cohort, observing high CIP2A levels in 18.2% of cases (40/220), and associated with tumor grade (p = 0.042), absence of ER (p < 0.001) and PR expression (p < 0.001), HER2 amplification (p = 0.023), and higher tumor proliferation rates measured using Ki-67 (p = 0.033).