Objective: Cytomorphologic differentiation of metastatic breast carcinoma from non breast metastases in cytological materials can be difficult. Current breast immunocytochemical markers have low sensitivities. Transcription factor GATA 3 is a promising marker for detecting breast differentiation in cytological materials. The aim of the study was to assess the diagnostic value of GATA 3 as a breast differentiation marker in metastatic cytological materials and to compare it with expression of mammaglobin and gross cystic disease fluid protein-15 (GCDFP-15).

Material and Method: We retrospectively retrieved 133 cases of metastatic breast carcinoma from the archive the of Cytology Unit between December 2013 and June 2015. They included 77 fine needle aspiration and 56 serous effusion samples. Forty-five cytological materials from non mammary metastatic tumors were used as a control. Immunostaining was performed on cell blocks for the presence of GATA 3, mammaglobin and GCDFP-15.

Results: GATA 3 nuclear staining was detected in 82.7% of metastatic breast carcinomas, and 11.1% of metastatic non mammary adenocarcinomas (p < 0.001). GATA 3 sensitivity, specificity, positive predictive value, negative predictive value and accuracy were 82.7%, 88.9%, 95.7%, 63.5% and 84.3%, respectively. Mammaglobin and GCDFP-15 staining of metastatic breast carcinoma cases was positive in 70.7% and 47.1%, respectively. GATA 3 staining was significantly higher compared with mammaglobin and GCDFP-15 (p< 0.001).

Conclusion: GATA 3 is more sensitive marker than mammaglobin and GCDFP-15 for diagnosing metastatic breast carcinoma in cytological cell block materials. Adding mammaglobin to GATA 3 resulted in improvement in its sensitivity. GATA 3 was occasionally positive in some metastatic non mammary carcinoma that may cause misdiagnosis.