Immunoexpression of SALL4 in Wilms tumors and developing kidney

SALL4 is a zinc finger transcription factor that plays a role in the maintainance and pluripotency of embryonic stem cell and is important in renal development where SALL4 mutations give rise to renal malformations. Because Wilms tumor recapitulates renal embryogenesis, we hypothesized that Wilms tumor cells may also express SALL4. We performed immunohistochemistry for SALL4 on tissue microarray sections of Wilms tumors, nephrogenic rests, and fetal renal cortices. Half (26 out of 52) of the Wilms tumors showed SALL4 immunoreactivity, ranging from strong and diffuse to focal and weak. Blastemal, epithelial, and combined blastemal and epithelial patterns of immunoreactivity were identified. No cases showed stromal staining. In the fetal kidney, SALL4 expression was restricted to the blastema and primitive epithelium at 15 weeks' gestation. SALL4 staining was not seen at later gestational ages, in non-neoplastic postnatal kidneys, or in nephrogenic rests. Our study is the first to demonstrate SALL4 immunoreactivity in Wilms tumors and in developing fetal kidney. The absence of SALL4 staining in nephrogenic rests, the presumed precursors of Wilms tumors, is intriguing and suggests that Wilms tumors have a pluripotency quality that may be lacking in nephrogenic rests.