Use of PAX8 and GATA3 in diagnosing sarcomatoid renal cell carcinoma and sarcomatoid urothelial carcinoma

Immunohistochemistry for PAX8 and GATA3 are sensitive markers for renal cell carcinoma and urothelial carcinoma, respectively. However, there are limited data on these markers in sarcomatoid renal cell carcinoma (SARCRCC) and sarcomatoid urothelial carcinoma (SARCUC). Tissue microarrays (TMAs) were constructed from 45 cases of SARCRCC and 45 cases of SARCUC of the lower urinary tract, with an additional 11 SARCUCs of the upper tract. PAX8 and GATA3 were also evaluated in TMAs from 161 sarcomas from other sites, 14 atypical epithelioid angiomyolipomas (AMLs) of the kidney, 23 bladder inflammatory myofibroblastic tumors (IMTs), and 2 bladder and 4 renal leiomyosarcomas. In the SARCRCC, PAX8 and GATA3 were positive in the sarcomatoid areas in 31 (69%) and 0 (0%) of cases, respectively. In the bladder SARCUC, GATA3 and PAX8 were positive in 14 (31%) and 2 (4%) of cases, respectively. Of the 11 SARCUCs of the upper urinary tract, 2 (18%) cases were PAX8 positive and 2 (18%) separate cases were GATA3 positive. Only 1 tumor present on the sarcoma TMAs, a Ewing sarcoma/primitive neuroectodermal tumor, was PAX8 positive, and all sarcomas were GATA3 negative. Of the AMLs, IMTs, and leiomyosarcoma, only 1 case of IMT showed moderate GATA3 positivity, and all were negative for PAX8. PAX8 can be used to distinguish SARCCRCC from atypical epithelioid AMLs and primary renal or retroperitoneal sarcomas. However, in a kidney/renal pelvic tumor, PAX8 shows overlap in staining between SARCUC and SARCRCC. GATA3 lacks sensitivity but is more specific for SARCUC.