Immunohistochemical differentiation of metastatic breast carcinomas from metastatic adenocarcinomas of other common primary sites

To test the possibility of immunohistochemical differentiation of cytostatically treatable metastatic breast carcinomas from other metastatic adenocarcinomas of unknown primary site, we studied a total of 328 metastatic adenocarcinomas including 35 bronchogenic, 26 pancreatic, 25 colonic, 39 gastric, 45 renal, 29 ovarian and 129 breast carcinomas with a panel of 13 commercially available monoclonal antibodies. The expression of gross cystic disease fluid protein 15 and/or oestrogen or progesterone receptors had a sensitivity of 0.83, a specificity of 0.93 and a predictive accuracy of 0.92 for carcinomas of the breast against all other carcinomas. Excluding ovarian carcinomas, this combination had a sensitivity, specificity and predictive accuracy for mammary carcinomas of 0.83, 0.98 and 0.98, respectively. Carcinoembryonic antigen and/or cytokeratin 20 identified bronchogenic, gastric, pancreatic and colorectal carcinomas versus breast carcinomas lacking gross cystic disease fluid protein 15 and oestrogen or progesterone receptors with a sensitivity, specificity and predictive accuracy of 0.82, 0.99 and 0.95, respectively. Vimentin differentiates renal cell carcinomas from gross cystic disease fluid protein 15 and oestrogen or progesterone receptor negative breast carcinomas with a sensitivity, specificity and predictive accuracy of 0.93, 0.82 and 0.84. Thus, it should be possible to differentiate most metastatic mammary carcinomas from metastatic adenocarcinomas of other common primary sites, even if the former lack expression of gross cystic disease fluid protein 15 and oestrogen or progesterone receptors.