ERBB2 and neoplasm: Thus, in the absence of chemotherapy, the probability of achieving a pCR if the tumour is HER2DX ERBB2 mRNA low or medium, which represents 62.5% of patients with HER2-positive/hormone receptor-positive disease, is only 4.0% (1/25), whereas the probability of achieving a pCR in HER2DX ERBB2 mRNA-high disease is 53.3% (8/15).