Pediatric adrenocortical tumors: Molecular events leading to insulin-like growth factor II gene overexpression

It has been previously shown that adrenocortical tumors (ACT) in adults exh ibit structural abnormalities in tumor DNA in approximately 30% of cases. T hese abnormalities involve chromosome 11p15 and include loss of heterozygos ity, paternal isodisomy, and overexpression of the gene for insulin-like gr owth factor II (IGF2), correlating with DNA demethylation at this locus. It has been hypothesized that these events occur late in the tumorigenic proc ess in adults and seem to correlate with a worse prognosis. We present 4 pe diatric cases of ACT diagnosed at 2.5 yr, 10 months, 12 yr, and 2.2 yr. All 4 patients presented with virilization, and 1 patient also showed signs an d symptoms of glucocorticoid excess. The youngest patient's maternal aunt h ad surgical excision of a more than 15-cm ACT 18 yr previously, but the aun t is doing well at age 23 yr. They all had surgical removal of their tumors . The 2.5-yr-old child also received chemotherapy and radiotherapy because of capsular rupture and, after 3 local recurrences, died 3.3 yr after initi al presentation. We investigated all 4 tumors for chromosome 11 structural abnormalities (11p15.5 to 11q23), IGF2 and H19 expression by competitive RT -PCR analysis, and IGF2 methylation patterns by Southern analysis. All 4 tu mors (100%) showed a combination of structural abnormalities at the 11p15 l ocus with mosaic loss of heterozygosity involving 11p. All tumors also had significantly increased IGF2 messenger ribonucleic acid levels relative to normal adrenal (up to 36-fold) and significant IGF2 demethylation (mean, 87 %). H19 messenger ribonucleic acid levels were undetectable in 3 of 4 tumor s, explained in part by mosaic loss of the actively expressed maternal alle le for this imprinted gene. By immunohistochemistry we were able to confirm increased IGF-II peptide levels within the tumor tissue in 10 pediatric pa tients, including the 4 patients described above. Concomitantly, we also ob served nuclear accumulation of p53, suggesting somatic mutations. For the 1 0-month-old patient, sequencing revealed a p53 germline mutation. We theref ore conclude that in pediatric ACT, structural abnormalities of tumor DNA a nd IGF2 overexpression as well as p53 mutations are very common and are the refore less useful for prognosis than in adults. Our findings support the t heory that pediatric ACT, whose IGF2 expression and steroidogenesis evoke t he phenotype of the fetal adrenal cortex, may arise because of defective ap optosis.