CA-549 is not diagnostically useful as an immunohistochemical marker for breast carcinoma

We evaluated BC4E549, a monoclonal antibody to CA-549, for use as an immunohistochemical marker to determine (1) differences in staining patterns between breast carcinoma and nonmalignant breast tissue specimens, (2) sensitivity and specificity of staining patterns for CA-549 in breast carcinoma vs other carcinomas, and (3) conservation of primary staining patterns in tumor metastases. We studied paraffin-embedded tissue specimens from 382 cases including nonmalignant breast tissue, endometrium, lung, pancreas, and thyroid gland; breast carcinoma; and adenocarcinomas of the colon, endometrium, lung, ovary, pancreas, and thyroid gland. Membranous staining was present in all nonmalignant breast tissue specimens and in most breast carcinoma tissue specimens. Diffuse cytoplasmic staining was more extensive in breast carcinomas than in benign processes. However, similar staining was also seen in normal and neoplastic tissue specimens obtained from a variety of other sites. Sensitivity and specificity of diffuse cytoplasmic staining for CA-549 in breast carcinoma relative to carcinomas from other sites studied were 78.6% and 77.4%, respectively. Staining patterns were not preserved from primary tumor to metastases in 67.4% of cases evaluated. We conclude that BC4E549 antibody to CA-549 is not a sufficiently sensitive or specific immunohistochemical marker in routinely processed tissue specimens to be useful in the clinical-diagnostic laboratory setting.