ODC1 and neoplasm: Thus, despite showing that the AG/GG genotypes lead to higher ODC1 transcript levels compared to the AA genotype in vitro, the difficulty in confirming this in primary tumor samples may be linked to a number of factors including: the relatively rare frequency of the A allele; tumor/stromal cell heterogeneity; and other determinants such as epigenetic modifications (at the level of DNA and/or chromatin) that can heavily affect ODC1 transcription.