Neuroendocrine Tumors/genetics; Neuroendocrine Tumors/metabolism; Signal Transduction/genetics; Wnt Proteins/genetics; Wnt Proteins/metabolism; beta Catenin/genetics; beta Catenin/metabolism; Adaptor Proteins, Signal Transducing/genetics; Adaptor Proteins, Signal Transducing/metabolism; Animals; Axin Protein/genetics; Axin Protein/metabolism; Cell Line, Tumor; Cell Nucleus/genetics; Cell Nucleus/metabolism; CpG Islands; Cytoplasm/genetics; Cytoplasm/metabolism; DNA Methylation; DNA Mutational Analysis/methods; Epigenesis, Genetic; Epigenomics/methods; Gene Expression/genetics; Genes, APC; Genes, Tumor Suppressor; Humans; Intercellular Signaling Peptides and Proteins/genetics; Intercellular Signaling Peptides and Proteins/metabolism; Male; Membrane Proteins/genetics; Membrane Proteins/metabolism; Mice; Mice, Nude; Mutation; Repressor Proteins/genetics; Repressor Proteins/metabolism; TCF Transcription Factors/genetics; TCF Transcription Factors/metabolism; Transcription, Genetic/genetics