The Human L1 Element: A Potential Biomarker in Cancer Prognosis, Current Status and Future Directions

The discovery of new biomarkers is a rapidly advancing area in cancer biology. The challenge of biomarker development for broad clinical use requires the translation of lab-based knowledge into clinical practice. The Long Interspersed Nuclear Elements-1 (LINE-1s or L1 elements) are active members of an autonomous family of non-LTR retrotransposons and occupy nearly 17% of the human genome. There is strong experimental evidence that the global hypomethylation of genomic DNA in cancer cells results in the activation of L1s and their expression is detectable at genome, transcriptome and proteome levels in human cancer cells. Thus, human L1s constitute a potential marker for cancer cells. In this review we have attempted to scrutinize L1 expression profiles in clinical cancer studies by undertaking a comprehensive systematic analysis of papers published in the field so far with a view to providing a more complete picture of the detection methods used, improvements achieved and potential future directions. Ultimately, we will try to evaluate the potential of L1s as a molecular marker in cancer detection.