Jonathan Frampton, Ph.D. global product manager Horizon Diagnostics
Companion diagnostics can determine which patients are likely to benefit from a drug, but risks still remain.
Companion diagnostics are bridging the gap between molecular diagnostics and therapeutics, helping to ensure that the right drug is provided to the right patient at the right time. Personalized medicine, with the aid of molecular diagnostics, is providing the exciting possibility of the delivery of cost-effective tailored therapies, based on an individual patient’s genetic code. This is particularly true in the case of cancer.
When applied correctly, companion diagnostics can help identify not only patients who are most likely to benefit from a particular therapeutic product, but also those likely to be at increased risk for serious side-effects as a result of treatment. Accurate diagnostics can also monitor response to treatment with a particular therapeutic product, to achieve improved safety.
As of October 2014, there were 19 FDA-authorized companion tests1 being used to support decisions on the particular therapy that a patient receives.
Through the use of companion diagnostics, decision-making on therapeutic application is shifting toward the molecular pathologist. This shift also profoundly impacts the burden of care, as any inaccuracies in the test process may result in incorrect treatment decisions. It is therefore the responsibility of every laboratory to insure that variability in workflows, assays, and methods is minimized in order to ensure correct diagnoses (Figure 1).
Genetic sequencing poses a particular risk, due to the large number of steps within a typical workflow and the many potential sources of unpredictability that may compound the test result (Figure 2). An error in a single step of the process can have dramatic impact. For example, quantity and efficiency in DNA extraction can be affected by a large number of factors such as pH, osmolality, time exposed to fixative, temperature, type of fixative, fixation time, and storage conditions, so it is vital that variability is continually accounted for or minimized.
The Significance of Colorectal Cancer
Colorectal cancer is the third most common cancer in men globally, and second in women, with over 1.4 million people each year being diagnosed with the disease and leading to an estimated 694,000 deaths.3 Diagnosis is currently carried out via sampling of areas of the colon where tumor development is suspected.
Epidermal growth factor receptor (EGFR) targeting therapies, such as Erbitux, have been developed for the treatment of patients with metastatic colorectal cancer, but aren’t universally effective. Around 30–40% of all colorectal tumors have mutations within the KRAS gene,4 and show poor response to Erbitux, with some patients experiencing significant side-effects. It is therefore essential to be able to differentiate between responders and nonresponders based on their genetics.
To address this need, in July 2012, the FDA approved the use of Qiagen’s therascreen KRAS RGQ PCR Kit to help determine the suitability of colorectal cancer patients for treatment with the drug Erbitux. As a result, the use of EGFR-targeting antibodies in metastatic colorectal cancer has now been restricted to patients with wild-type KRAS tumors. It is therefore critical that healthcare providers take every precaution available to them to ensure these tests generate accurate results.
Proficiency Testing Schemes
Proficiency testing schemes have been established around the world to help drive standardization and improvements in diagnostic testing. These programs have a big part to play in ensuring that the results of molecular testing investigations are reliable and comparable, with a particular focus on education and the promotion of best practices, and carrying out independent audits on laboratories.
In order to address the challenges identified through proficiency schemes, reliable genetic reference materials are required to determine quality and accuracy of molecular assays, enabling improvement and increased consistency across the board.
A variety of different sources of genetic reference materials is available (Figure 3). Synthetic reference standards provide a renewable source (e.g., oligonucleotides/plasmids), but amplify more easily than their equivalent templates from cellular sources, which can create false confidence in molecular assay workflows. Patient-derived materials have been the traditional option; however they come with a high degree of variability and are limited in supply.
Although the use of reference standards has dramatically increased laboratories’ performance worldwide, driving up quality and accuracy of tests, there is still considerable room for improvement.
Genetically Defined Reference Standards
To optimally support standardization in diagnostics, laboratories need reference materials that truly reflect patient samples, with a defined copy number and precise allele burden, mimicking genome complexity and tumor cell genetics, but that are also renewable, consistent, and reproducible. Horizon Diagnostics’ HDx™ Reference Standards have been developed to fit these criteria, with mutations precisely engineered into highly characterized parental cell lines. The “normal” cell lines have fully defined cancer mutations, resulting in perfect heterozygotes that endogenously contain the mutation of interest.
Recently, a worldwide external quality assessment (EQA) proficiency testing scheme launched a series of large-scale audits to determine accuracy of a range of diagnostic tests. The EQA assessed the performance of 59 laboratories in eight different countries, in three rounds of tests. The results were concerning in that they showed only 70% (30% error rate) of participants were able to correctly identify the KRAS mutational status in all samples, for accurate colorectal cancer diagnosis.2
The EQA proficiency testing scheme highlights the issues currently faced with variability in DNA extraction from tumor biopsies. Both false-positive and false-negative results negatively affect patient care. Lack of standardization is a major source of error in molecular biology laboratories. Increased implementation of proficiency testing schemes, aided by a renewable, genetically defined source of reference materials, will help provide an unprecedented level of control to laboratories for tumor profiling.
1. List of Cleared or Approved Companion Diagnostics Devices (In Vitro and Imaging Tools), The United States Food and Drug Administration (FDA). Accessed: http://www.fda.gov/MedicalDevices/ProductsandMedicalProcedures/InVitroDiagnostics/ucm301431.htm on 17th October 2014
2. World Cancer Report 2014. World Health Organization. 2014. pp. Chapter 1.1. ISBN 9283204298.
3. Brink M, de Goeij AF, Weijenberg MP et al. K-ras oncogene mutations in sporadic colorectal cancer in The Netherlands Cohort Study. Carcinogenesis 2003;24:703–710.
4. External Quality Assessment for KRAS Testing Is Needed: Setup of a European Program and Report of the First Joined Regional Quality Assessment Rounds, The Oncologist 2011;16:467–478
This article was originally published in the November 5 issue of Clinical OMICs. For more content like this and details on how to get a free subscription to this digital publication, go to www.clinicalomics.com.