To examine if the variation in PTEN expression found by immunohistochemistry may be due to methylation of the PTEN promoter in some of the tumor cells, we analyzed tumor DNA for methylation in the PTEN promoter, in comparison with two genes known to be methylated in neuroblastoma (RASSF1A, MTHFR [39, 40]. This evidence concerns the gene RASSF1 and neoplasm.