The field of precision medicine is rooted in biomarker guided therapy. These biomarkers come in various forms as well as are categorized depending on use cases. Within oncology where nearly all of the companion diagnostic approvals lie, the biomarkers tend to either be DNA, RNA or protein based. However, metabolites as well as phenotypic markers exist and can possibly be leveraged to guide therapy.
Interestingly, the only non-oncology CDx to date is a MRI based device!
The general categories of markers are outlined below. Asterisks denote the class of markers that hold potential for use as a companion diagnostic.
- Susceptibility/Risk – marker to determine risk of disease occurrence in “healthy” individuals.
- Diagnostic – marker to diagnose disease or subtype.
- Prognostic – marker indicating an outcome (e.g. survival, progression, etc) not linked to a treatment.
- Predictive* – marker indicating an outcome linked to a specific treatment.
- Response/Monitoring* – marker gauging response to a treatment (e.g. surgery or therapy)
- Recurrence – marker to monitor the re-emergence of the disease
The FDA clearly defines a CDx to be a device that can:
- identify patients who are most likely to benefit from a particular therapeutic product;
- identify patients likely to be at increased risk for serious side effects as a result of treatment with a particular therapeutic product; or
- monitor response to treatment with a particular therapeutic product for the purpose of adjusting treatment to achieve improved safety or effectiveness.
Reference: https://www.fda.gov/medical-devices/in-vitro-diagnostics/companion-diagnostics
We see trials and approvals focusing on the first bullet point which is testing of patients prior to administration of therapy. The positive (or negative) result from the CDx device informs the benefit of therapy to the patient with the biomarker and guides whether the patient may receive the therapy. The last bullet point of an approved monitoring assay that may guide dosing of a specific therapeutic has yet to be seen. This would be an assay that tracks longitudinally pre- and post-therapy administration for which the results would be used to alter therapy. Based on the trend of ultra-sensitive monitoring assays currently in development and in trials, expectation is there will be a next wave of post-therapy induction monitoring CDx’s coming soon.
