Three's a Crowd
There's just one hitch: Ordering all of these tests individually would be expensive, time-consuming (if ordered sequentially as many healthcare systems do), and require sample preparations for each separate test. A single, unified test system would address these problems, but the way to create one isn't clear-cut, either.
The tests themselves don't necessarily lend themselves to multiplexing as some are immunohistochemistry-based (most of Dako's and Ventana's lineup), while others are nucleic-acid based (MDxHealth and Dako). There are also competing tests for the same characteristic, such as Herceptest, CB11, and 4B5 antibodies for detecting Her2; some papers have even suggested using these tests to verify each other.
The problem is not intractable, however. Technician time is expensive, and automation could provide the answer in preparing multiple tests simultaneously at lower cost—the overall mass of the samples necessary isn't so large that a single sample cannot be split up to be used for multiple protocols, and some nucleic acid tests are easily combined into a microarray. Patent pooling could be used to bring together the necessary IP, and data collected would permit better understanding of cancer mechanisms.
If a unified test could be designed to recommend the top three most effective treatments for a given patient, it would assist patients and doctors while saving money in the long run by eschewing ineffective treatments. Even dosages and adjuvants may be affected, as some nontarget polymorphisms affect pharmacokinetics and efficacy of small molecule drugs and antibodies. Such a test would be valuable for everyone . A given treatment might apply to 20% of the patient population, but the test would be appropriate for 100%.
Whether a unified test appears or not, the information granted by companion diagnostics will remain valuable in both product development and patient treatment. If knowledge is power, then companion diagnostics are powerful friends, and it never hurts to have powerful friends.