Subtype-specific FBXW7 mutation and MYCN copy number gain in Wilms' tumor

Abstract

Purpose: Wilms' tumor (WT), the most common pediatric renal malignancy, is associated with mutations in several well-characterized genes, most notably WT1, CTNNB1, WTX, and TP53. However, the majority of cases do not harbor mutations in these genes. We hypothesized that additional drivers of tumor behavior would be contained within areas of consistent genomic copy number change, especially those associated with the WT risk groups defined by the International Society of Paediatric Oncology (SIOP).

Experimental design: We analyzed high-resolution (Affymetrix 250K single nucleotide polymorphism array) genomic copy number profiles of over 100 tumors from selected risk groups treated under the SIOP protocols, further characterizing genes of interest by sequencing, Multiplex Ligation-dependent Probe Amplification, or fluorescence in situ hybridization.

Results: We identified FBXW7, an E3 ubiquitin ligase component, as a novel Wilms' tumor gene, mutated or deleted in approximately 4% of tumors examined. Strikingly, 3 of 14 (21%) of tumors with epithelial type histology after neoadjuvant chemotherapy had FBXW7 aberrations, whereas a fourth WT patient had germline mutations in both FBXW7 and WT1. We also showed that MYCN copy number gain, detected in 9 of 104 (8.7%) of cases, is relatively common in WT and significantly more so in tumors of the high risk diffuse anaplastic subtype (6 of 19, 32%).

Conclusions: Because MYCN is itself a target of FBXW7-mediated ubiquitination and degradation, these results suggest that a common pathway is dysregulated by different mechanisms in various WT subtypes. Emerging therapies that target MYCN, which is amplified in several other pediatric cancers, may therefore be of value in high risk Wilms' tumor.

Copyright 2010 AACR.

Figures

Figure 1

FBXW7 mutations in Wilms tumour. (a) Chromosome 4 copy number profiles (log2 scale) for WT samples RMH-2990 and RMH-2594. The position of the FBXW7 gene is indicated with an arrow; FBXW7-specific probe positions are in red. (b) Extent of the 4q31.3 deletions relative to NCBI RefSeq genes and Affymetrix 250k SNP probe positions. (c) Sequence chromatograms for FBXW7 mutations detected in WT samples RMH-1549 and RMH-4714.

Figure 2

MYCN gain in Wilms tumour. (a) Chromosome 2 copy number profiles (log2 scale) for four examples of WT with gain at the MCYN locus. The position of the MYCN gene is indicated with an arrow. (b) Extent of the 2p24.3 gains relative to NCBI RefSeq genes and Affymetrix 250k SNP probe positions. (c)MYCN amplification (red) detected by FISH with reference to LAF copy number control on 2q (green). (d)MYCN copy number measured by MLPA (mean of two different MYCN-specific probes, linear scale) for eight samples with gain detected by the Affymetrix array, and four control samples without 2p24.3 aberrations in their array profiles. A copy number of 2.4 (1.2x diploid) was taken as the threshold of gain (dashed line).

Figure 3

Haematoxylin and eosin stained paraffin-embedded sections showing histology of tumours with FBXW7 or MYCN aberrations. (a) RMH-2990 (100x magnification). Epithelial type WT showing poorly and moderately differentiated tubules with some papillary structures. (b) RMH-1549 (100x). Epithelial type WT showing highly differentiated tubules. (c) RMH-2967 (100x). Diffuse anaplastic WT; examples of anaplastic cells are indicated with arrows. (d) RMH-2969 (100x) Diffuse anaplastic WT; examples of anaplastic cells are indicated with arrows. (e) RMH-2967 (600x). Diffuse anaplastic WT with areas of rhabdoid-like histology including prominent nucleoli (indicated with arrows). (f) RMH-2969 (600x). Diffuse anaplastic WT with areas of rhabdoid-like histology including prominent nucleoli (indicated with arrows).