A predictive biomarker helps determine which patients are most likely to benefit from a specific treatment option. Predictive diagnostics can provide information about how well a treatment is likely to work in a particular patient or about the likelihood of that treatment causing an unwanted side effect.
Not all patients with the same diagnosed health disorder have the same biological mechanism of disease. Predictive biomarkers can help doctors determine what is happening in a particular patient based on their health condition’s particular biological mechanism.
Drugs that have a different effect depending on the different biological mechanisms associated with a disease are called targeted therapies. Targeted therapies are paired with a "companion" diagnostic test, which indicates the presence of a specific biomarker that is associated with the specific mechanism of disease in a particular patient. Patients that test positive with the companion diagnostic are eligible for treatment with the targeted therapy. The targeted therapeutic is specifically designed to affect the particular molecular mechanism of their disease, indicated by the companion diagnostic test, thus, likely making it more effective than other non-targeted treatment options.
The approach is especially promising in cancer and rare genetic disorders. These diseases are very often driven by known genetic mutations. Targeted therapies are available for colorectal, lung and breast cancers, among others. You can use the link provided in the "Examples" section to learn more about how personalized medicine applies to lung cancer.
Percentage of Tumors Driven by Known Genetic Mutations
Source: The Advisory Board, The Journey to Personalized Medicine, 2016 (https://www.advisory.com/research/oncology-roundtable/resources/2013/posters/the-journey-to-personalized-medicine).
Pharmacogenomics is the study of how genes influence a person’s response to drugs. Pharmacogenomic tests measure biomarkers that help predict what medications at what doses will be safest and most effective for individuals based on their genetic makeup.
Many drugs are prescribed as “one-size-fits-all,” meaning all patients are prescribed the same formulation at the same dose. But these drugs don’t work the same way for everyone. Pharmacogenomic tests help predict who will benefit from a medication, and who will have potentially severe side effects.
This approach is especially useful, for example, in prescribing blood thinners for patients with heart disease or hematological disorders. Most of these patients benefit from treatment with blood thinners, however, some patients with particular variations of some genes that play a role in how these drugs are processed in the body are at a much greater risk of severe side effects associated with these drugs. On one hand, some blood thinning drugs will not be very effective in patients with a genetic makeup that allows them to break down these drugs too quickly. These patients will be at a greater risk of excess blood clotting and stroke. On the other hand, patients with a genetic makeup that causes them to break down these drugs too slowly compared to other patients are at a much greater risk of severe bleeding.