IGF2 and cancer: However, 1 isoform of the non-imprinted C1D and 3 isoforms of the imprinted H19 had higher expression in the cell lines where they were monoallelically expressed, suggesting separate regulation of allelic expression and overall expression of H19 and C1D. H19 is an important negative regulator of IGF2 expression, with important implications in cancer [1, 2, 4, 8, 137].