To ascertain the implications of loss of imprinting (LOI) of the insulin-like growth factor II gene (IGF2) for carcinogenesis, the precise frequency of LOI in colorectal carcinoma was examined using a laser capture microdissection method, and compared to the matched normal colorectal mucosa. LOI was examined by PCR-restriction fragment length polymorphism in combination with direct sequencing. The status was assigned as imprinting when PCR-RFLP showed only one band or sequence with a single peak, otherwise cases were classified as LOI. LOI was found in 13 of 24 informative cases of carcinoma (54%), which was higher than the ratios reported previously. LOI was also found in the normal colorectal mucosae in 14 cases (58%). The LOIs in carcinomas and in the normal mucosae were closely correlated: 10 of 13 LOI-positive carcinomas showed LOI in the matched normal mucosae. These results suggest that LOI of IGF2 in colorectal carcinoma and LOI in the background mucosa play important roles in carcinogenesis.

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