Immunohistochemical markers in the identification of metastatic breast cancer.

A panel of nine monoclonal and polyclonal antibodies were tested regarding specificity for metastatic breast cancer. A hundred metastatic tumors were stained, 50 of breast origin and 50 of other origins. Antibodies used were anti-alpha-lactalbumin, anti-lactoferrin, anti-casein, E29 (Dako-EMA), anti-secretory component, anti-gross cystic disease fluid protein (GCDFP15), BRST1, BRST2, and MC5. Analyses of the results were performed using chi-square and logistic regression. Positivity for MC5, BRST1, BRST2, lactoferrin, EMA, and GCDFP15 was significantly higher in tumors of breast origin than in others (p less than 0.05). Analyses of the whole panel indicated that GCDEP15 and MC5 were the best markers for identification of breast cancer metastases. When both were positive (58% of breast origin cases), the predicted probability of breast origin was 98%, compared to only 5% when both were negative. Comparison of anti-GCDFP15 with BRST2, a monoclonal antibody against the same protein, showed a slightly better sensitivity of the former, and a similar degree of specificity for breast tissue. In conclusion, a panel of antibodies can be used to securely differentiate metastatic breast cancer from other cancers in a large number of metastatic tumors of unknown origin.