The Galleri test is also called the Multi-Cancer Early Detection (MCED) test. It is, at this point, still considered to be an experimental test designed for the early detection of multiple cancers. It requires merely a blood sample and payment of the $949 fee. Insurance doesn’t cover it. I wrote a blog about it in October 2022, and nothing has changed about it except for intense scrutiny of the test.
The Galleri test is the invention of a California biotechnology company called Grail. The company has a European presence known as Grail Europe which has come under a lot of criticism for “overhyping” the accuracy of the test. Grail claims Galleri detects the cell-free DNA of at least 50 different cancers thus giving doctors a tool that will detect cancer earlier and more accurately. The National Health Service (NHS), the government-run health care system of Great Britain, has been particularly skeptical of the benefits of Galleri testing.
The “turn-over rate” of cancer cells is very rapid. In other words they grow and multiply rapidly and have a shorter life than normal cells. When cancer cells die, they break down and release cell-free DNA (cfDNA) into the blood stream. Each type of cfDNA is specific to the type of cancer from which it comes. When Galleri detects the presence of cfDNA, and gives doctors a clue where to look for the problem (cancer). The test is particularly sensitive for detecting cancers of the colon and rectum (82%), esophagus (85%), head and neck (86%), liver and bile ducts (93.5%), pancreas (84%), and ovary (83%). Bladder (35%), stomach (67%), and lymphomas (56%) cancers are much less readily detected.
The British National Health Service has been very concerned that this test may be over-rated, and the hype is lining the pockets of the company and individuals who have developed and promoted it. The BNHS has been concerned about the high rate of false positives and the fact that early stage (Stage I) cancers are still very poorly detected—only 16.8% of the time. As a London cancer researcher said, “These results are strikingly low!” They also found that “in patients already known to have cancer the test detected only 43.9% of Stage I-III cancers.
If it detects fewer than 20% of Stage I cancers, it is still better than the 6% detection rate for other routine screening methods detection of Stage I disease? Galleri is a better option, but for $949 is a mere 10% improvement worth it? Sensitivity is significant for Stage IV disease, but when cancers reach Stage IV, they are probably clinically evident and already diagnosed, negating the need for Galleri testing.
Researchers also admit that a positive MCED test indicates microscopic metastases in every case and means “incurable distant metastatic disease” is present. They also admit that “despite early detection, the course of the disease is unaltered, and patients die at the same time as they would without the test.” They then say “the test provides no overall clinical benefit.” So this test needs further investigation.
I think the jury still needs to collaborate on Galleri testing. The lack of a high rate of detection of Stage I and II Cancers is disturbing. It brings to question the cost-effectiveness of this test and whether or not it will lower mortality rates. It doesn’t seem that it will.
So before you pay $949 for this controversial test, wait awhile to see if further study brings about any better detection rates. I know some doctors are ordering it because a good friend in California had one. His results were negative, which I hope for his sake is an accurate result.
Reference: Pyzocha NT. Galleri Test for the Detection of Cancer. Am Fam Phys 2022;106(4):459-460.
Nicholson BD et al. Multi-Cancer early detection test in symptomatic patients referred for cancer investigation in England and Wakes: a large scale observational study. Lancet Oncology 2023 July;24(7):733-743.
McCartney, M, Cohen D. Galleri promises to detect multiple cancers—but new evidence casts doubt on this much hyped blood test. BMJ 2024;386:q1706.
Callister MEJ, Crosbie EJ, Crosbie PAJ, Robbins RA. Evaluating multi-cancer early detection tests: an argument for the outcome of recurrence-updated stage. Brit J Cancer 2023;129:1209-1211
