Identification, Validation and Implementation of Blastemal Biomarkers in Wilms Tumour

Sammanfattning: The aim of this thesis has been to establish biomarkers for the blastemal element in Wilms tumour (WT) – the most common paediatric kidney cancer. Blastema is, together with epithelium and stroma, one of the three common histological elements of WT. WTs dominated by blastema after preoperative chemotherapy are classified as high risk tumours.
According to the SIOP2001 protocol used in most European countries today, there is no recommendation of using molecular markers for WT risk stratification and this assessment is based on clinico-histological parameters alone. Patients with high risk tumours receive an extensive treatment, which may results in severe long term side effects. To secure an accurate estimation of the amount of blastemal elements a marker for detection of WT blastemal cells could be a useful tool, indirectly leading to a more precise risk estimation.
Literature studies and gene expression data were used to identify potential markers for WT blastema. The protein expressions for candidate markers were evaluated by immunofluorescence on WT cell lines and paraffin-embedded WT tissue sections. Tissue microarrays were constructed to improve the efficiency of this process and the most prominent marker was also validated by immunohistochemical protein staining, to prepare it for clinical use.
The two proteins found to have the most specific expression in blastemal cells were SIX1 and CITED1. These proteins are transcription factors expressed during kidney development and both were shown to be highly expressed in the blastemal element of WT (89% and 100%, of WT cases, respectively). SIX1 and CITED1 also displayed some expression in the epithelial (25% and 64%, respectively) and stromal (52% and 48%, respectively) elements. Since particularly CITED1 was highly expressed in epithelial components, SIX1 was selected for further clinical evaluation.
In summary, SIX1 appeared to be a useful marker for defining blastemal elements in WT. SIX1 does not replace a pathologist’s evaluation and should only be used as a tool to help give a more accurate estimation of the extent of the blastemal elements in WT.