This antibody recognizes a protein of 185kDa, identified as the second member (cerbB-2/HER-2) of the c-erbB family. This rabbit monoclonal antibody is directed against the cytoplasmic domain of the human c-erbB-2 protein. The c-erbB-2 is closely related in structure to the epidermal growth factor receptor. The c-erbB-2 protein is over-expressed in a variety of carcinomas, especially those of breast and ovary. Immunohistochemical staining correlates with gene amplification. Studies have shown that c-erbB-2 positive breast cancer usually correlates with negative staining for estrogen and progesterone receptors; thus a poorer predictive outcome is correlated with c-erbB-2 staining.