A gene signature or gene expression signature is a single or combined group of genes in a cell with a uniquely characteristic pattern of gene expression [1] that occurs as a result of an altered or unaltered biological process or pathogenic medical condition. [2] This is not to be confused with the concept of gene expression profiling. Activating pathways in a regular physiological process or a physiological response to a stimulus results in a cascade of signal transduction and interactions that elicit altered levels of gene expression, which is classified as the gene signature of that physiological process or response. [3] The clinical applications of gene signatures breakdown into prognostic, diagnostic [4] [5] and predictive signatures. The phenotypes that may theoretically be defined by a gene expression signature range from those that predict the survival or prognosis of an individual with a disease, those that are used to differentiate between different subtypes of a disease, to those that predict activation of a particular pathway. Ideally, gene signatures can be used to select a group of patients [6] for whom a particular treatment will be effective. [7] [8]
In 1995, 2 studies conducted identified unique approaches to analyzing global gene expression of a genome which collectively promoted the value of identifying and analyzing gene signatures for physiological relevance. The first study reports a technique that improves expressed sequence tag (EST) analysis, known as Serial Analysis of Gene Expression (SAGE) that hinged on sequencing and quantifying mRNA samples which acquired levels of gene expression that eventually revealed characteristic gene expression patterns. [9]
The second study identified a technique that is now widely known as the microarray which quantifies complementary DNA (cDNA) hybridization on a glass slide to analyze the expression of many genes in parallel. [10] These studies drew greater attention to the wealth of information that analysis of gene signatures bear that may or may not be physiologically relevant.
Pressing forward, the latter technique has revolutionized research in genetics and DNA chip technology [11] as it is a widely adopted technique to profile gene expression signatures such that these physiological responses can be cataloged [12] in repositories such as NCBI Gene Expression Omnibus. This catalogue of prognostic, diagnostic and predictive gene expression signatures allow for predictions of onset of pathogenic diseases in patients, [13] tumour and cancer classification, [14] and enhanced therapeutic strategies that predict the optimal target candidates subjects and genes. [15]
Today, microarrays and other quantitative methods such as RNA-seq that encompass gene expression profiling, are moving towards promotion of re-analysis and integration of the large, publicly available database of gene expression signatures and profiles to uncover the full threshold of information these expression signatures hold. [16]
Prognostic refers to predicting the likely outcome or course of a disease. Classifying a biological phenotype or medical condition based on a specific gene signature or multiple gene signatures, can serve as a prognostic biomarker for the associated phenotype or condition. This concept termed prognostic gene signature, serves to offer insight into the overall outcome of the condition regardless of therapeutic intervention. [17] Several studies have been conducted with focus on identifying prognostic gene signatures with the hopes of improving the diagnostic methods and therapeutic courses adopted in a clinical settings. It is important to note that prognostic gene signatures are not a target of therapy; they offer additional information to consider when discussing details such as duration or dosage or drug sensitivity etc. in therapeutic intervention. The criteria a gene signature must meet to be deemed a prognostic marker include demonstration of its association with the outcomes of the condition, reproducibility and validation of its association in an independent group of patients and lastly, the prognostic value must demonstrate independence from other standard factors in a multivariate analysis. [3] The applications of these prognostic signatures include prognostic assays for breast cancer, [18] [19] hepatocellular carcinoma, [20] leukaemia [21] and are continually being developed for other types of cancers and disorders as well.
A diagnostic gene signature serves as a biomarker that distinguishes phenotypically similar medical conditions that have a threshold of severity consisting of mild, moderate or severe phenotypes. [5] Establishing verified methods of diagnosing clinically indolent and significant cases allows practitioners to provide more accurate care and therapeutic options that range from no therapy, preventative care to symptomatic relief. These diagnostic signatures also allow for a more accurate representation of test samples used in research. [6] Similar to the procedure of validation of prognostic gene signature, a criterion exists for classifying a gene signature as a biomarker for a disorder or diseases outlined by Chau et al. [22] [23]
A predictive gene signature is similar to a predictive biomarker, where it predicts the effect of treatment in patients or study participants that exhibit a particular disease phenotype. A predictive gene signature unlike a prognostic gene signature can be a target for therapy. [17] The information predictive signatures provide are more rigorous than that of prognostic signatures as they are based on treatment groups with therapeutic intervention on the likely benefit from treatment, completely independent of prognosis. [24] Predictive gene signatures addresses the paramount need for ways to personalize and tailor therapeutic intervention in diseases. These signatures have implications in facilitating personalized medicine through identification of more novel therapeutic targets and identifying the most qualified subjects for optimal benefit of specific treatments. [3] [25] [26]
Urokinase, also known as urokinase-type plasminogen activator (uPA), is a serine protease present in humans and other animals. The human urokinase protein was discovered, but not named, by McFarlane and Pilling in 1947. Urokinase was originally isolated from human urine, and it is also present in the blood and in the extracellular matrix of many tissues. The primary physiological substrate of this enzyme is plasminogen, which is an inactive form (zymogen) of the serine protease plasmin. Activation of plasmin triggers a proteolytic cascade that, depending on the physiological environment, participates in thrombolysis or extracellular matrix degradation. This cascade had been involved in vascular diseases and cancer progression.
Personalized medicine, also referred to as precision medicine, is a medical model that separates people into different groups—with medical decisions, practices, interventions and/or products being tailored to the individual patient based on their predicted response or risk of disease. The terms personalized medicine, precision medicine, stratified medicine and P4 medicine are used interchangeably to describe this concept though some authors and organisations use these expressions separately to indicate particular nuances.
MammaPrint is a prognostic and predictive diagnostic test for early stage breast cancer patients that assess the risk that a tumor will metastasize to other parts of the body. It gives a binary result, high-risk or low-risk classification, and helps physicians determine whether or not a patient will benefit from chemotherapy. Women with a low risk result can safely forego chemotherapy without decreasing likelihood of disease free survival. MammaPrint is part of the personalized medicine portfolio marketed by Agendia.
Biomarker discovery is a medical term describing the process by which biomarkers are discovered. Many commonly used blood tests in medicine are biomarkers. There is interest in biomarker discovery on the part of the pharmaceutical industry; blood-test or other biomarkers could serve as intermediate markers of disease in clinical trials, and as possible drug targets.
In biomedical contexts, a biomarker, or biological marker, is a measurable indicator of some biological state or condition. Biomarkers are often measured and evaluated using blood, urine, or soft tissues to examine normal biological processes, pathogenic processes, or pharmacologic responses to a therapeutic intervention. Biomarkers are used in many scientific fields.
In medicine, a biomarker is a measurable indicator of the severity or presence of some disease state. It may be defined as a "cellular, biochemical or molecular alteration in cells, tissues or fluids that can be measured and evaluated to indicate normal biological processes, pathogenic processes, or pharmacological responses to a therapeutic intervention." More generally a biomarker is anything that can be used as an indicator of a particular disease state or some other physiological state of an organism. According to the WHO, the indicator may be chemical, physical, or biological in nature - and the measurement may be functional, physiological, biochemical, cellular, or molecular.
Autoimmune lymphoproliferative syndrome (ALPS) is a form of lymphoproliferative disorder (LPDs). It affects lymphocyte apoptosis.
The miR-92 microRNAs are short single stranded non-protein coding RNA fragments initially discovered incorporated into an RNP complex with a proposed role of processing RNA molecules and further RNP assembly. Mir-92 has been mapped to the human genome as part of a larger cluster at chromosome 13q31.3, where it is 22 nucleotides in length but exists in the genome as part of a longer precursor sequence. There is an exact replica of the mir-92 precursor on the X chromosome. MicroRNAs are endogenous triggers of the RNAi pathway which involves several ribonucleic proteins (RNPs) dedicated to repressing mRNA molecules via translation inhibition and/or induction of mRNA cleavage. miRNAs are themselves matured from their long RNA precursors by ribonucleic proteins as part of a 2 step biogenesis mechanism involving RNA polymerase 2.
The estrogen receptor test (ERT) uses the estrogen receptor (ER) tumor marker that allows for immunohistochemical techniques to be performed for diagnostic purposes. Immunohistochemistry (IHC) methods involve the selective identification of antigen proteins by exploiting these antigen-antibody relationships to characterize your analyte of interest. Previously, the ligand binding assay has been used to determine ER activity. However, this method was limited because of the large quantities of fresh tissue needed for each assay. IHC serves as a more efficient method as this technique allows for the tissue morphology to be observed in a tumor-specific manner. This increases the practicability of this technique as in many cases, patients’ tissue samples are limited in the applications of biomarker analysis. Anti-estrogen receptor antibodies were among the first of biomarkers that introduced a semi-quantitative assessment of the ER activity. Today, ER analysis is one of many routinely performed immunohistochemical assays performed to classify the hormone receptor status and to serve as a means of insight into the determination of cancer prognosis and management.
The basal-like carcinoma is a recently proposed subtype of breast cancer defined by its gene expression and protein expression profile.
A circulating tumor cell (CTC) is a cell that has shed into the vasculature or lymphatics from a primary tumor and is carried around the body in the blood circulation. CTCs can extravasate and become seeds for the subsequent growth of additional tumors (metastases) in distant organs, a mechanism that is responsible for the vast majority of cancer-related deaths. The detection and analysis of CTCs can assist early patient prognoses and determine appropriate tailored treatments. Currently, there is one FDA-approved method for CTC detection, CellSearch, which is used to diagnose breast, colorectal and prostate cancer.
microRNA 21 also known as hsa-mir-21 or miRNA21 is a mammalian microRNA that is encoded by the MIR21 gene.
Cancer is a category of disease characterized by uncontrolled cell growth and proliferation. For cancer to develop, genes regulating cell growth and differentiation must be altered; these mutations are then maintained through subsequent cell divisions and are thus present in all cancerous cells. Gene expression profiling is a technique used in molecular biology to query the expression of thousands of genes simultaneously. In the context of cancer, gene expression profiling has been used to more accurately classify tumors. The information derived from gene expression profiling often helps in predicting the patient's clinical outcome.
DirectHit is a pharmacodiagnostic test used to determine the tumor sensitivity or resistance to drug regimens recommended for the treatment of breast cancer by the National Comprehensive Cancer Network. It is a noninvasive test performed on small amounts of tissue removed during the original surgery lumpectomy, mastectomy, or core biopsy. DirectHit was developed by CCC Diagnostics Inc., a biotechnology company established by former researchers from Johns Hopkins University. DirectHit was launched on 14 January 2010. Currently, it is the only available test for predicting treatment outcomes for anticancer chemotherapy drugs for breast cancer.
Anil Potti is a physician and former Duke University associate professor and cancer researcher, focusing on oncogenomics. He, along with Joseph Nevins, are at the center of a research fabrication scandal at Duke University. On 9 November 2015, the Office of Research Integrity (ORI) found that Potti had engaged in research misconduct. According to Potti's voluntary settlement agreement with ORI, Potti can continue to perform research with the requirement of supervision until year 2020, while he "neither admits nor denies ORI's findings of research misconduct." As of 2020 Potti, who is employed at the Cancer Center of North Dakota, has had 11 of his research publications retracted, one publication has received an expression of concern, and two others have been corrected.
A cancer biomarker refers to a substance or process that is indicative of the presence of cancer in the body. A biomarker may be a molecule secreted by a tumor or a specific response of the body to the presence of cancer. Genetic, epigenetic, proteomic, glycomic, and imaging biomarkers can be used for cancer diagnosis, prognosis, and epidemiology. Ideally, such biomarkers can be assayed in non-invasively collected biofluids like blood or serum.
In the field of medicine, radiomics is a method that extracts a large number of features from medical images using data-characterisation algorithms. These features, termed radiomic features, have the potential to uncover tumoral patterns and characteristics that fail to be appreciated by the naked eye. The hypothesis of radiomics is that the distinctive imaging features between disease forms may be useful for predicting prognosis and therapeutic response for various cancer types, thus providing valuable information for personalized therapy. Radiomics emerged from the medical fields of radiology and oncology and is the most advanced in applications within these fields. However, the technique can be applied to any medical study where a pathological process can be imaged.
Prognostic markers are biomarkers used to measure the progress of a disease in the patient sample. Prognostic markers are useful to stratify the patients into groups, guiding towards precise medicine discovery. The widely used prognostic markers in cancers include stage, size, grade, node and metastasis. In addition to these common markers, there are prognostic markers specific to different cancer types. For example estrogen level, progesterone and HER2 are markers specific to breast cancer patients. There is evidence showing that genes behaving as tumor suppressors or carcinogens could act as prognostic markers due to altered gene expression or mutation. Besides genetic biomarkers, there are also biomarkers that are detected in plasma or body fluid which can be metabolic or protein biomarkers.
The Immunologic Constant of Rejection (ICR), is a notion introduced by biologists to group a shared set of genes expressed in tissue destructive-pathogenic conditions like cancer and infection, along a diverse set of physiological circumstances of tissue damage or organ failure, including autoimmune disease or allograft rejection. The identification of shared mechanisms and phenotypes by distinct immune pathologies, marked as a hallmarks or biomarkers, aids in the identification of novel treatment options, without necessarily assessing patients phenomenologies individually.
Oncometabolism is the field of study that focuses on the metabolic changes that occur in cells that make up the tumor microenvironment (TME) and accompany oncogenesis and tumor progression toward a neoplastic state.