Differential diagnosis of collecting duct carcinoma (CDC) from invasive upper tract urothelial carcinoma (UTUC) can be challenging. PAX8 and p63 are 2 markers often used in this setting. GATA binding protein 3 (GATA3) is a marker of urothelial differentiation. We investigated GATA3 expression in CDC and UTUC and its use in this differential. Eighteen CDC and 25 UTUC cases were used to build 2 tissue microarrays. GATA3, p63, and PAX8 nuclear expression was evaluated using standard immunohistochemistry. Staining intensity and percentage of positive cells were assessed. Sensitivity, specificity, and positive and negative predictive values of the markers and their combination were also evaluated. We found GATA3 positivity in 22 (88%) of 25 UTUCs and 1(6%) of 18 CDCs. The median GATA3 extent of expression was higher in UTUC than in CDC (74% versus 0%, P =.00). We found p63 positivity in 23 (92%) of 25 UTUCs and 2 (11%) of 18 CDCs. PAX8 was positive in 3 (12%) of 25 UTUCs and all (100%) CDCs. GATA3 sensitivity and specificity for UTUC were 88% and 94%, respectively. p63 sensitivity and specificity for UTUC were 92% and 89%, respectively. The p63+/ PAX8- profile showed higher sensitivity for UTUC than did the GATA3+/PAX8- profile (80% versus 76%), Both showed a specificity of 100% for UTUC. GATA3+ or p63+/PAX8- sensitivity and specificity for UTUC were 84% and 100%, respectively. Immunohistochemical expression of GATA3 was higher in UTUC, suggesting a potential role for distinguishing UTUC from CDC. Adding this marker to the combination panel of p63 and PAX8 might improve its performance in the diagnosis of epithelial neoplasms involving the renal sinus. (C) 2013 Elsevier Inc. All rights reserved.