Estrogen Receptor Mutations and Changes in Estrogen Receptor and Progesterone Receptor Protein Expression in Metastatic or Recurrent Breast Cancer

To investigate the frequency of estrogen receptor (ER) gene mutation in metastatic or recurrent breast cancer, metastatic lymph nodes or recurrent breast cancer tissue from 35 patients with ER‐positive primary tumors were screened for mutations in the hormone‐binding domain of the ER gene by sequence analysis. Four missense mutations, Val316Ile, Gly344Val, Ala430Val and Gly494Val, were identified in these lesions. Second, to clarify whether there is any disparity in hormone receptor status between primary and metastatic or recurrent tumors, we immunohistochemically studied 117 specimens including the above 35 specimens obtained from metastatic or recurrent breast cancer patients using monoclonal anti‐ER and progesterone receptor (PgR) antibodies. Although hormone receptor status, especially ER, was highly maintained through disease progression, negative change in PgR expression at relapse (33%) was identified more frequently than in metastatic lymph nodes (6.7%). Therefore, it was suggested that development of PgR‐negative phenotype might correlate with disease progression in some breast cancer patients. These results suggest that ER mutations in metastatic or recurrent breast cancer may be more frequent than in primary lesions, irrespective of high maintenance of ER protein expression through disease progression.