Utility of mammaglobin and gross cystic disease fluid protein-15 (GCDFP-15) in confirming a breast origin for recurrent tumors.

There are limited data that compare the utility of immunohistochemical detection of mammaglobin with Gross Cystic Disease Fluid Protein-15 (GCDFP-15) in locally recurrent and metastatic breast cancers. Forty-three local and 72 distant recurrences of breast cancer, 8 metastatic lesions to the breast from other organs, and 30 metastases from non-breast primaries were immunohistochemically stained with mammaglobin and GCDFP-15 antibodies. Mammaglobin was expressed in 55 (47.8%) and GCDFP-15 detected in 13 (11.3%) locally and distantly recurrent breast cancers. A higher percentage of tumor cells was stained with mammaglobin at greater staining intensity than GCDFP-15, for both metastatic and locally recurrent breast cancers. The difference in staining intensity as well as mean percentage of tumor cells stained for both markers was statistically significant (p < 0.005). Metastases to the breast from other organs and metastatic lesions from non-breast primaries were uniformly negative for both mammaglobin and GCDFP-15. Our study demonstrates that immunohistochemical analysis of mammaglobin is superior to GCDFP-15 in detecting a tumor of breast origin, and can be incorporated into immunohistochemical panels evaluating tumors from unknown primary sites.