Drugs and Diagnostics Make Good Companions for Patient Outcomes
Companion Diagnostics Open the Way for Personalized Therapy
Catherine Shaffer | 2017-05-31
Traditionally, diagnosis and treatment of disease have been separate procedures, with the choice of treatment being the therapy that has provided the best benefit for the most people. Increased understanding of tumor biology as well as advances in molecular diagnostics and imaging, however, have made it possible to personalize therapy, giving doctors powerful tools to choose the best therapy for an individual patient from a range of options. Increasingly, drug therapies are being paired with customized diagnostic tests known as companion diagnostics. These tests enable proper selection of patients for a specific drug therapy and thereby help to improve the overall therapeutic efficiency. For example, there are about 20 such tests currently approved in the U.S., with many more in development.1 The tests are typically based on genetic markers, but some are also based on proteins or medical imaging. Most of the progress has been in the area of cancer, where matching the right drug and the right patient can be crucial.
Genetic Markers for Cancer Treatment
The HER2 gene, for example, is a model companion diagnostic marker. The gene contributes to the growth of aggressive breast cancer when it is expressed at abnormally high levels in the body. Testing of the corresponding HER2 protein status has become part of the standard battery of diagnostic procedures for breast cancer, because there are now several drugs that specifically target HER2-positive tumors. Indeed, the concept has been revolutionary for the clinical management of the disease.
While in the past, being positive for HER2 worsened a patient’s prognosis, because of the aggressive overgrowth caused by the HER2 gene, personalized therapy using HER2 as a companion diagnostic marker has now brought survival rates in line with patients who do not overexpress that gene. One recent study shows an almost 90-percent overall five-year survival rate for early-stage breast cancer patients positive for HER2.2 There are now companion diagnostic tests available for personalized treatment of other tumors like ovarian cancer, non-small cell lung carcinoma, and colorectal cancer.
New Tech for New Tests
Newer technologies in drug development open up new possibilities for companion diagnostics. For example, antibody-drug conjugates (which combine an antibody with a standard drug) target specific surface antigens on various tumors. Of course, it would be necessary to know if these antigens are at all present on the cancer cells before starting the therapy. One approach is through analyzing circulating tumor cells in the blood with novel automated laboratory platforms, which have shown promise as a mode of detection of such antigen-positive cancers in recent investigations.3
Imaging technologies like positron emission tomography (PET) and single-photon emission computed tomography (SPECT) can also be used to create a companion diagnostic test. Imaging can provide a whole-body view on the entire tumor load and is a noninvasive alternative to tests based on tissue or fluid samples. In addition, imaging tests can often provide faster results than those based on nucleic acids or proteins.
Molecular Imaging on the Rise
One technology, which is in clinical trials in Europe and the United States, aims at imaging the cellular receptor for folic acid with a SPECT scanner and a specific radioimaging probe.4 Cancer cells need folic acid to rapidly grow and thus often overexpress the receptor. When such folate-receptor positive malignancies are detected through molecular imaging, patients could possibly be treated more successfully with a corresponding receptor-targeted drug.
Diagnostics and therapeutics merge even more when drug candidates are modified through the addition of a fluorescence-imaging marker for optical imaging. The fluorescent drug “lights up” like a neon sign when it encounters a cancer cell. For example, this approach has been tested for lymphoma cells in laboratory studies with mice.5 In the future, it might allow doctors to see the drug fighting cancer in real time and assess a response in an individual patient.
About the Author
Catherine Shaffer is a science writer specializing in biotechnology and pharmaceuticals. A former lab scientist with a master’s degree in biochemistry, she has covered advances in drug technology for over 15 years. Catherine is based in Ann Arbor, Michigan, USA.
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1U.S. Food and Drug Administration. List of Cleared or Approved Companion Diagnostic Devices (www.fda.gov/MedicalDevices/ProductsandMedicalProcedures/InVitroDiagnostics/ucm301431.htm), accessed 03 July 2015
2Zurawska U, Baribeau D, Giilck S et al. (2013). Outcomes of her2-positive early-stage breast cancer in the trastuzumab era: A population-based study of Canadian patients. Current Oncology 20:e539-45.
3Xiaolei Q, Beas H, Matias M et al. (2015) Development of a circulating tumor cell assay for use in selecting patients for a novel antibody-drug conjugate therapy. J Clin Oncol 33, suppl: abstr e22022
4Maurer AH, Elsinga P, Fanti S et al. (2014) Imaging the folate receptor on cancer cells with 99mTc-etarfolatide: properties, clinical use, and future potential of folate receptor imaging. J Nucl Med. 55:701-4
5Turetsky A (2014) Companion Imaging Probes and Diagnostic Devices for B-Cell Lymphoma. Doctoral dissertation, Harvard University (http://dash.harvard.edu/handle/1/13094356, accessed 03 July, 2015)
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