Dispelling the Myths of Genetic Tests
Genetic tests are now increasingly being used for the screening and diagnosis of both cancer and non-cancer conditions. Those for cancer differ from genetic tests for non-cancer conditions in the relatively larger number of tests for somatic mutations. Somatic mutations are genetic mutations that occur in somatic cells after conception. As cancer develops, somatic mutations are common if growth regulators in the cell are damaged by toxins, radiation, random error in cell division, and other factors. Somatic mutations cannot be inherited and only affect the lineage of cells derived from mutated cells. In contrast, mutations in germ cells will affect all the cells in the body, and are often the result of acquired mutations from a parent.
Okay – so what is the point of genetic tests?
Clinical Applications of Genetic Tests
As with many tests, there are multiple applications of the test and this is no different in the case of onco-specific genetic tests. The outcome of a genetic test can be categorized into 5 different ‘buckets’ (see below):
- Diagnostic test: this is used to confirm or aid in the diagnosis of the particular disease.
- Prognostic test: information from the test can be used to determine or predict the aggressiveness of the disease or overall outcome of the disease at the time of initial diagnosis and prior to initiation of treatment. Prognostic information can then be used to determine a particular or individualized treatment plan.
- Predictive test: information from the test can be used to determine or predict the response of the disease or overall outcome of the disease with treatment.
- Recurrence test: to detect disease recurrence in a patient who has already been diagnosed and treated for cancer.
- Monitoring test: test used to monitor tumor and/or patient response to treatment.
So How Does this fit in with Personalized Medicine?
Previously, for a big pharma-company to produce a drug, the resulting drug that was eventually produced needed to be a blockbuster with billions in revenue. Unfortunately (or fortunately!), many patients are not the same and have different outcomes and consequently different treatments are needed. Despite research budgets increasing the number of drugs is static as of 2015. Understanding the disease and working out that many diseases have a genetic origin and since the completion of the human genome project in 2003 we know more now than ever. The ‘fingerprints’ of genetic information now tell us more than ever, including: the 5 outcomes (above) as well as the medicine’s eventual affect.
This information is proving invaluable for the identification as well as the efficacy of the drug. The cost of sequencing a genome has fallen very rapidly, beyond even Moore’s law.
A great example is Cresotonib on NSCLC; taking only 7 years compared to the average of 14 years. Originating first in 2004 from the identification of targets the success can be seen in a £230m annual return on a first investment of £500m. The drug however, is suitable for a limited number of patients.
What is personalized medicine? Ultimately: Genetic screening matches the right drug to the right patient at the right time.