ESR1 and breast neoplasm: No other significant association was observed between the different levels of Ki-67 immunoreactivity in Responder and Non Responder breast tumors and histologic type (P = 0.1), tumor size (P = 0.7), lymph node status (P = 0.2), hormone receptor expression (ER, P = 0.8; PR, P = 0.3), or HER2 status (P = 0.2).