Congratulations, you turned 50! It’s time for your colonoscopy.
Today it looks like most routine screening colonoscopies may become a relic of the past…due to new blood tests that are being developed.
Currently, for those with moderate risk of developing colorectal cancer (CRC), stool tests are an alternative to colonoscopies. The most common are the FIT (fecal immunochemical test), and the more expensive Cologuard test. Both tests look for altered DNA, namely, the presence of abnormal cells or blood which may indicate cancer or precancerous tumors. The FIT has a 79% accuracy rate at detecting colon cancer and needs to be repeated annually. Additionally, the FIT test is prone to false positives, which then require a colonoscopy, so we are not out of the woods yet. Cologuard boasts a 92% accuracy rate, so it only has to be repeated every 3 years, but its higher cost means that it is often not covered by insurance.
But it gets better, a simple blood-test is likely to be approved to test for CRC. Guardant Health, Inc, announced the completion of its US premarket approval application for its Shield blood test to screen for CRC. Three rival companies are developing similar blood tests.
If the blood tests do as well as expected, basic screening colonoscopies and the current FIT and Cologuard could be mostly phased out in favor of these blood tests.
A blood test for cancer screening has been the ‘holy grail’ for years.
Currently blood tests are the best tests for blood cancers such as Hodgkin and Non-Hodgkin lymphoma, leukemia, and multiple myeloma. But the goal is to create blood tests that can screen for other cancers.
In 2020, Johns Hopkins designed a study to see whether it was possible to use a blood test to detect cancers before symptoms appeared. Fragments of erroneous DNA, cells broken off from tumors, antigens, and certain proteins get released into the bloodstream as tumors start to grow; these are called tumor markers. A total of 16 gene mutations and a number of proteins related to cancer can currently be identified from the blood, with more research underway.
Tumor markers have been identified for liver, thyroid, esophageal, breast, lung, stomach, pancreatic, testicular, prostate, and ovarian cancers.
A carcinoembryonic antigen blood test can potentially detect asymptomatic cancer at several organ sites, but to date it is only a warning sign, tissue and scanning tests are necessary for confirmation. The PSA (Prostate-specific antigen) test, used to detect prostate cancer, is a tumor marker test that is searching for a specific antigen. But it’s not perfect and will not find all prostate cancers.
Some tests are searching for cells that have been shed by the cancerous tumor into the bloodstream. Circulating tumor cells (CTCs) are another indicator of malignant cells in the body. The cells that are identified in the blood can be used to trace back to where they originated from and find the part of the body where the tumor might be.
But there actually is a relatively comprehensive test, called the Multi-Cancer Early Detection Blood Test (MCED), already on the market (Galleri) that has not yet been approved by the FDA. Due to its expense and reliability (both false positives and false negatives) it is not covered by most insurance. But for those with a $1,000 and concern about cancer, it can potentially detect 50 cancers. At this time, it is good at detecting Stage 4 cancers and less capable of detecting Stages 1 and 2. And it is prone to errors. Research showed that a “positive” cancer result, happened in 45% of those actually having cancer.
The test is based on the fact that all cells, both cancer and noncancer, shed cfDNA (cell-free DNA) into the bloodstream. This MCED test analyzes the cfDNA. Some studies are encouraging.
Yet, due to the false positive (indicates cancer when there is no cancer) and false negative (indicates no cancer when there is cancer) rates doctors aren’t always sure about what to do with the information. The company claims that it can detect more than 50 types of cancers, of which 45 don’t have a recommended screening test available. But it can result in unnecessary screening tests or other patients who have cancer believing themselves to be cancer-free. Its maker recommends that it be used to supplement other testing.
In January, the FDA approved a cancer detection blood test, called the OverC Multi-Cancer Detection Blood Test (MCDBT) to aid in detecting cancer for people from 50-75 years of age with average risk. It is expected to aid detection of esophageal, liver, lung, ovarian, and pancreatic cancers.
So, there is a lot of research and excitement about our blood giving up some of cancers’ secrets…and for those of us over 50; few of us will miss the colonoscopy.
It is something that we can tell our grandchildren about…if we wish them to leave.
Angela Rieck, a Caroline County native, received her PhD in Mathematical Psychology from the University of Maryland and worked as a scientist at Bell Labs, and other high-tech companies in New Jersey before retiring as a corporate executive. Angela and her dogs divide their time between St Michaels and Key West Florida. Her daughter lives and works in New York City.