ESR1 and neoplasm: Similarly, in the CA15-3-high subset, the frequencies of larger tumor size (p < 0.0001), lymph node metastasis (p < 0.0001), ER negativity (p = 0.021), PgR negativity (p = 0.013), HER2 positivity (p = 0.024), and chemotherapy administration (p = 0.0011) were significantly higher.