K-Ras, H-Ras, N-Ras and B-Raf mutation and expression analysis in Wilms tumors: association with tumor growth.

Nephroblastoma (Wilms tumor) is a kidney neoplasia, predominately occurring at very young age, resulting from the malignant transformation of renal stem cells. The Ras proto-oncogenes and B-Raf are members of an intracellular cascade pathway, which regulates cell growth and differentiation, and ultimately cancer development. Our objective was to determine the mutation rate and to measure the mRNA levels of the three Ras genes and of B-Raf in formalin-fixed paraffin-embedded tissue samples from 32 patients with nephroblastoma and 10 controls. No mutations were detected in the four studied genes among our Wilms tumors cases, while Ras and B-Raf expression was higher in malignant samples versus controls. Statistical analysis revealed a positive correlation of K-Ras (p < 0.001) and B-Raf (p = 0.006) with tumor size, a negative correlation of K-Ras (p = 0.041) and H-Ras (p = 0.033) with the percentage of tissue necrosis, and an association of N-Ras (p = 0.047) and B-Raf (p = 0.044) with tissue histology. From the above, we deduce that although Ras and B-Raf mutations are rare events in Wilms tumors, their expression pattern suggests that they play an important role in the development and progression of this malignancy.