MMP9 and lung cancer: Although the differences in allele transcription caused by polymorphisms in the MMP promoters are subtle when compared to, for example, oncogene overexpression [46,51], specific genotypes have appeared to affect the concentrations of MMP-2 and MMP-9, which when increased may result over a lifetime in an increased susceptibility to lung cancer, a more aggressive course of the disease, and poorer patient survival outcomes.