Companion Diagnostics are medical products/services that define the use of other medical products, drugs, and other devices. An in vitro diagnostic test is a specific test that measures a relevant biomarker and has to be confirmed in order to deliver the required medical care. A companion diagnostic is required to make sure that a medical product is safe and effective. A companion diagnostic is therefore a subset of biomarker-oriented tests, which cover all diagnostic tests. These specific tests have now been around since the mid-1990s and around 90% of companion diagnostics are for oncology treatment.
Companion Diagnostics are developed along with a new experimental drug and it is in the form of a test that checks if the profile of a patient is safe enough for the said drug. Some of the ways a companion diagnostic may be useful and necessary in order to appropriately and effectively use a therapeutic.
- It helps in selecting patients for whom the drug would be effective.
- companion diagnostic helps to identify patients who should not be treated with the drug because of a high risk of adverse events and toxicity.
- It helps with improving personalised medicine and targeted drug therapy.
- It helps healthcare professionals to know about the benefit and risk profile of a drug or treatment for a patient.
Many oncology drugs are quite toxic and tend to have a positive effect on only a fraction of the population with a particular expression or genetic makeup of the disease. Even patients with similar cancer diagnoses do not respond the same way to an experimental drug, in terms of safety, efficacy, and treatment. Responses are widely variable and almost 75% of cancer patients do not respond favourably to the same prescribed drug.
It is very similar to Complementary Diagnostics. Complementary Diagnostics are also a set of diagnostic tests that help to determine the effectiveness of a drug or product. However, in contrast to a companion diagnostic, a complementary diagnostic is not a necessity for using the drug, so it is optional. Information about a complementary diagnostic is usually included in the therapeutic product labeling.
Companion diagnostics is a technique within the field of pharmacogenomics. Pharmacogenomics is the study of understanding how the whole genome (the entire genetic framework and not just a singular gene) of an individual responds to the drug. Pharmacogenomics is a crucial part of offering safe and effective treatments in the care of cancer patients, where there is the need to treat a malignant disease aggressively and quickly without causing any fatal side effects to the patient. Most drugs that are used with a companion diagnostic test are used to target specific tumor mutations.
Herceptin is a drug that treats metastatic breast cancer. When the drug was still in clinical trials, an immunohistochemistry test, HercepTest, was developed and approved simultaneously with another drug trastuzumab. HerCepTest is a semi-quantitative immunocytochemical assay that finds out the HER2 (Human Epidermal Growth Factor Receptor 2) protein overexpression in breast cancer tissues. Once the drug was approved, the kit was available to determine which patients should receive trastuzumab.
In colorectal cancer, cetuximab and panitumumab are given to patients with tumors that overexpress the epidermal growth factor receptor (EGFR). The companion diagnostic test EGFR pharmDx is used to determine the level of overexpressed EGFR in the biopsy samples and was used to identify patients eligible for the necessary drug trials. KRAS mutations are now considered an important biomarker for several cancers. Tests to determine the presence of these mutations are now mentioned in several cancer drug labels to avoid unnecessary exposure to potentially toxic drugs.
Personalized medicine, where the effects of treatment are determined for an individual patient, has been a significant part of cancer treatment for several decades. Biomarkers and molecular diagnostics have helped to shape the necessary companion diagnostics which helps to improve health outcomes for patients. As new clinical trial designs work to improve scientific, especially oncology research, cancer patients greatly benefit from new diagnostic tests. These new biologic and gene therapies provide steady improvements in survival and quality of life for diseases that have previously had a very poor prognosis.