As people age, some of their normal blood cells naturally pick up small mutations that have nothing to do with cancer. This is called CHIP. It's common, especially in older adults. Without separating non-cancer mutations from cancer mutations, which many tests do not do, you risk an improper treatment pathway or an incorrect diagnosis.
This isn't rare. In one study of patients with advanced cancer, about half of the mutations found in blood came from these aging blood cells rather than from the tumor. Without a way to tell the two apart, a patient can be recommended a targeted drug for a mutation that is not actually in their tumor.
The fix is straightforward: ask your oncologist if the blood test they plan to use can tell the difference and remove CHIP from the decision-making process.
For Example
A 72-year-old man with prostate cancer has a blood test that reports a mutation in a DNA-repair gene like ATM or CHEK2. That result could point toward a class of targeted drugs called PARP inhibitors, a treatment approach built for tumors driven by this kind of mutation. But the mutation actually comes from his aging blood cells rather than his tumor. If that difference is missed, he could end up on an aggressive targeted therapy aimed at a mutation his cancer never had, while the mutation actually driving his tumor goes unaddressed.
Questions To Ask Your Oncologist
- Can this blood test tell the difference between CHIP mutations and cancer mutations?
- If it cannot, how will you know which mutations came from my cancer?
- Can both tissue and blood be tested in my case?