Strong androgen receptor expression is not useful in distinguishing GATA3 + metastases.

GATA binding protein 3 (GATA3) immunohistochemical expression is commonly considered to be a sensitive and specific diagnostic marker for breast and urothelial carcinomas in surgical pathology practice. However, since its expression has been also demonstrated in other tumors, GATA3 should be better used in conjunction with other immunohistochemical markers to establish tumor primitivity in metastatic setting. Interestingly, GATA3 expression seems to be significantly correlated with androgen receptor (AR) expression in breast carcinoma. In addition, strong AR expression -defined as immunohistochemical positivity in more than 60% of tumor cells- was suggested to be 100% specific for breast origin in GATA3+ metastases. The aim of this study was to verify whether strong AR expression may actually be useful to determine primivity in GATA3+ metastatic setting. Thus, we investigated AR and GATA3 immuno-expression in a cohort of metastatic tumors derived from urothelial, breast, endometrial and salivary gland carcinomas. We did not find any GATA3 or AR expression in the metastases from endometrial or salivary gland carcinomas, while GATA3 expression was seen in the majority of metastases from urothelial or breast carcinomas. In addition, strong AR expression was seen in 73% and in 47% of metastatic breast and urothelial carcinomas, respectively. On the whole, our findings confirm that GATA3 is sensitive and specific for breast and urothelial origin in metastatic setting. According to our results, strong AR expression is not useful to distinguish breast from urothelial primitivity, as previously suggested.