February 2018, Dr Chee L Khoo
“Doc, is there a test for cancer?” I’m sure you have many a patient asking for a blood test to screen for cancer. Some of you may be tempted to order a CEA or a CA-125 without being familiar with their sensitivities and specificities (that’s another story on another day). An international group of researchers recently described a blood test, called CancerSEEK which purportedly can detect eight common cancers. What’s different about this screening test?
Cancer cells are dying all the time, and some of their DNA will end up in the bloodstream. This test looks for 16 of these cancer DNA. Also, cancers make certain proteins, and so eight such proteins are also included in the test. With some sophisticated software to look at the patterns of which genes and which proteins, the type of cancer can be determined. For example, ovarian cancer will have different genes and proteins that light up compared with liver cancer. Therefore, this test can not only detect cancer, but also help identify which tissue is involved; hence, this is often referred to as a “liquid biopsy.”
To test the CancerSEEK test, researchers looked at 1005 patients who had known cancers between stage I and III i.e cancers that had not metastasized yet. The cancers chosen were ovary, liver, stomach, pancreas, oesophagus, colo-rectal, lung, and breast. In the US, these cancers account fot 60% of all cancer deaths.
Overall, the tests were able to detect 70% of the cancers but the detection rates were different for different cancers. Ovarian and liver were best at 98% but breast were only detected in 33% of the time. Stage I cancers were detected at 43%, stage II cancers at 73%, and stage III cancers at 78%. Of the stage I cancers, liver cancer was detected at 100%, whereas oesophageal cancer was the lowest, at 20%.
There is a lot more work to be done on finding better DNA fragments and more tissue specific proteins as well as better algorithm in analysing the patterns. Then, the tests need to be road tested on patients without known cancers to determine their sensitivity and specificity.
These are early but promising days.
Access the abstract here.
Joshua D. Cohen, Lu Li, Yuxuan Wang, Christopher Thoburn, Bahman Afsari, Ludmila Danilova, Christopher Dou. Detection and localization of surgically resectable cancers with a multi-analyte blood test. Science 18 Jan 2018: