In particular, the loss of ER, PgR and HER-2 expression has been described by Duchnoswka et al. [22], and it has been found in about 20% of patients by Thomson et al. [23]; Schrijver et al. [24] showed that ER conversion rates were significantly higher in brain than in liver BC metastases, while PgR conversion rates were much more negligible in the central nervous system than in bone metastases. This evidence concerns the gene ESR1 and breast cancer.