Loss of imprinting and abnormal expression of the insulin-like growth factor 2 gene in gastric cancer.

This study examined the frequency of loss of imprinting (LOI) and expression of the insulin-like growth factor 2 (IGF2) gene, and their relationship to selected clinical and pathological factors, in a well defined series of 90 Chinese patients with gastric cancer (GC) and 90 matched patients (controls) diagnosed with nonmalignant conditions. Using peripheral blood and gastric tissue samples, polymerase chain reaction-based assays and restriction endonuclease (Apa I) digestion revealed 33 GC patients and 21 controls to be Apa I informative. LOI of IGF2 was positive in 48.5% (16/33) of primary GC tumor tissues, in 21.2% (7/33) of histologically normal adjacent gastric mucosa (AM) and in 12.1% (4/33) of distant gastric mucosa (DM), and in 15.2% (5/33) of peripheral blood lymphocytes (PBLs). The prevalence of IGF2 LOI in PBL was not statistically different between GC patients (5/33, 15.2%) and control subjects (2/21, 9.5%), P = 0.69. Although patients who were found to have LOI of IGF2 were more likely to have advanced stage gastric tumors (P = 0.04), no statistically significant differences in survival were found based on imprinting status. IGF2 LOI was associated with an increased expression of IGF2 level in both tumors (P < 0.01) and blood (P < 0.01). The results of this study implicate IGF2 LOI in the molecular pathogenesis of GC, most likely through increased IGF2 expression. Although the precise molecular mechanisms by which LOI of IGF2 increases GC risk require further study, LOI of IGF2 may be a potentially important clinical epigenetic marker to identify individuals at increased risk for gastric malignancy.