GATA3 expression in small cell carcinoma of bladder and prostate and its potential role in determining primary tumor origin.

GATA3 is a sensitive marker for urothelial carcinoma. We here evaluate, for the first time, GATA3 expression in small cell carcinoma of bladder and prostate and assess its utility in the differential diagnosis with small cell carcinoma of lung primary. Archival tissues from 60 small cell carcinomas (12 bladder, 15 lung, and 33 prostate primary cases) were used to build 2 tissue microarrays. We also assessed whole slide sections from 10 additional primary small cell carcinomas of bladder. GATA3 nuclear expression was evaluated using standard immunohistochemistry. Intensity (weak, moderate, and strong) and extent of expression were assessed in each tissue microarray spot. Extent positivity was categorized as focal (1%-25%), multifocal (>25%), and diffuse (>75%). Nuclear GATA3 expression was encountered in 7 bladder (7/22, 32%) and 2 lung (2/15, 13%) small cell carcinomas. All 33 primary prostate small cell carcinomas were negative. Among bladder tumors, strong and diffuse (>75%) GATA3 labeling was seen in 3 cases (3/22, 14%); focal positivity was observed in the 4 remaining cases (4/22, 18%). Both positive lung cases had only focal positivity. Our study is the first to reveal GATA3 expression in the small subset of lung small cell carcinoma that should be taken into consideration in assigning site of origin in advanced small cell carcinoma cases. Our novel finding of GATA3 positivity in one-third of bladder small cell carcinoma is of potential value in differentiating small cell carcinomas of prostate origin from those of bladder origin.