Tumor biomarkers are molecules often produced by the tumor itself or the host system in response to the tumor and provide the biological material to determine the risk of getting cancer, to detect cancer, to classify cancer, or to provide insight into prognosis and therefore a therapeutic advantage. Tumor biomarkers include cancer-specific mutations or changes in gene expression or promoter methylation, which can result in alterations in protein expression. Because cancer cells shed DNA and RNA in the circulation, a phenomenon rarely seen in healthy individuals, tumor-specific genetic changes such as promoter methylation, gene mutations or circulating small RNAs are detectable in nucleic acids prepared from plasma or other body fluids. Biomarker proteins, either overly abundant or variant proteins can be detectable in the circulation as the free, shed proteins or as novel autoantibodies to such proteins; the latter indicating that the host immune system can be exploited as biosensor of the disease. In addition, tumor-specific biochemical changes result in post-translational modification of proteins via glycosylation or phosphorylation providing a variety of biomarker molecules. Cancer-related biochemical changes often affect measurable metabolic variations within a cell or organism which may be powerful biomarkers.
Cancer biomarkers are discovered and utilized with a specific purpose in mind such as the (a) early detection of cancer, (b) diagnosis, (c) prognosis, (d) response to anticancer therapies or (e) cancer recurrence (). Cancer cells provide the biomarker material that can lead to their own detection, which then provides the opportunity for their non-invasive detection in body fluids and tissues so as to reveal the presence of tumors or the level of tumor burden. Biomarkers for cancer diagnosis, prognosis, and response to therapy have become possible through elegant studies of specific carcinogenic mechanisms [1
] leading to the development of clinical tests capable of predicting the optimal or targeted therapeutic approach for a given cancer. Alternatively, well-powered biomarker discovery projects have also led to clinical tests for therapeutic decisions for some cancers [4
There is an emerging expectation that panels of biomarker analytes rather than single markers will be required to have sufficient sensitivity and specificity for the diagnosis or prognosis of cancer. This realization became apparent from the failure of single biomarkers to be adapted for clinical practice. The need for panels of biomarkers, specific for each cancer, is based on the experience from decades of molecular oncology research that has demonstrated molecular complexity of human carcinogenesis even within single cancer sites.
Biomarkers hold promise not only for diagnostic devices and to improve the effectiveness of clinical interventions but also to stratify oncology patients to the most appropriate treatment. However, early detection must provide a patient with more efficient delivery of healthcare, which ultimately should translate to better survival. For example, early detection technologies applied to population-based screening for cancer of the cervix, colon, and breast have resulted in reductions in disease-associated mortalities from cancers that are deadly if allowed to progress to an advanced stage. These screening approaches are technology driven but have proven that early detection will reduce the morbidity and mortality from cancer.
Biomarkers can provide prognostic information of disease enabling intervention with the appropriate therapeutic agent and early decisions for corrections of cancer treatment. There has been a burst of novel technologies that are being used to discover and validate tumor biomarkers individually and where necessary in panels or combinations of biomarkers. Although biomarkers have the potential to provide personalized diagnostic, prognostic and therapeutic information for the individual patient, the devices to implement them clinically must ensure that healthcare providers have clear algorithms for step by step implementation to their patients.