Boto A, et al. - An exploration was pursued of the classical markers of breast differentiation and hormonal signaling in order to identify which correlated strongest with GATA3 expression in breast cancer, which in turn would assist in accurately determining the breast origin in the case of the GATA3 positive tumor of unknown origin. A strong connection was disclosed between androgen receptor (AR) expression with GATA3 in breast cancer, especially in tumors with lobular morphology. Data illustrated that strong AR expression (>60% of tumor cells) was an excellent test to rule out urothelial carcinoma in the GATA3+ metastatic setting (specificity 100%) and would effectively determine the breast origin in around 50% of cases.