KRAS and cancer: However, the differences between Let-7 target mRNAs in each of these models can be quite disparate; e.g. KRAS has a larger effect on tumorigenesis than does HMGA2 in a non-small cell lung cancer model [49], whereas HMGA2 appears to have a much larger role in other cancer models [28,50–53], likely as a modifier of chromatin structure and gene expression [54–57].