Development of New Rabbit Monoclonal Antibody to Estrogen Receptor

Evaluation of estrogen and progesterone receptors in breast cancer is widely used for the prediction of the response to endocrine therapy and as a biologic parameter closely related to disease prognosis. Immunohistochemistry is considered a specific, sensitive, and economic method for the determination of estrogen receptor/progesterone receptor status. The authors developed the first rabbit antiestrogen receptor monoclonal antibody (clone SP1) used in immunohistochemistry on formalin-fixed, paraffin-embedded tissue sections especially from breast carcinomas. This new antibody, compared with currently available antiestrogen receptor antibodies, has important advantages, including its reactivity even without heat-based antigen retrieval of fixed, embedded tissue sections in immunohistochemistry, and the predominance of nuclear immunostaining with only a very low cytoplasmic signal. A comparative study of immunohistochemistry on 61 histologic specimens from breast cancer cases showed that SP1 yields the same results as the well-known, standardized mouse monoclonal antibody to estrogen receptor (clone 1D5). Antibody affinity of SP1 is 8 times higher than that of 1D5. Thus, SP1 may prove of great value in the assessment of estrogen receptor status in human breast cancer.