Methods and compositions related to the use of Mobile Element Insertions and their adjacent genomic sequences. Methods using MEIs as markers for cellular proliferation, as targets for pharmaceuticals, as markers for tissue fingerprinting and in related methods and compositions are disclosed herein. Methods and compositions relate to the detection, treatment and ongoing monitoring of cell proliferation events, cancer, and deleterious effects of mobile elements in aging, and to the selection, use and monitoring of the success of treatment regimens to address these conditions.