Promising Blood Tests for Early Cancer Detection
New research indicates that ongoing evaluations of blood tests may yield hopeful results for early cancer screening, particularly in identifying various cancers at stages when treatment could be more effective.
Developing an ideal early screening method for cancer has been an ongoing struggle in healthcare. However, recent findings point to blood tests currently under investigation as showing potential for diagnosing cancers earlier than usual.
These multi-cancer early detection (MCED) tests analyze DNA fragments shed by cancers into the bloodstream.
“These tests can check for many different types of cancer simultaneously,” explained Dr. Rebecca Kaltman, who leads the Inova Saville Cancer Screening and Prevention Center at the Inova Schar Cancer Institute in Fairfax, Virginia.
So far, the U.S. Preventative Task Force has only approved five tests for early cancer detection: mammograms for breast cancer, colonoscopies for colon cancer, Pap smears for cervical cancer, prostate-specific antigen (PSA) tests for prostate cancer, and low-dose CT scans for lung cancer.
The absence of reliable screening tests for over 100 cancer types—like pancreatic, liver, and ovarian—often results in late-stage diagnoses when treatments become challenging.
Research shows that about 70% of cancer fatalities stem from cancers that lack early screening options.
More than 800 participants from Schar took part in the national Pathfinder II study related to the Galleri test developed by Grail.
Another MCED test, Cancerguard, is also in the process of seeking U.S. Food and Drug Administration approval. This test is produced by Exact Sciences.
Accuracy and False Positives
During an MCED test, results will either come back positive or negative. If positive, it indicates that a possible cancer signal was detected, Kaltman noted.
The Galleri test typically identifies one or two potential origin sites for the cancer, which will then require further follow-up assessments to verify if the positive result is indeed accurate.
Just like with other early screening techniques, a positive result doesn’t necessarily mean cancer is present.
“With mammograms, when there’s a concern, it’s often not cancer,” Kaltman commented. “Literature varies, but about 15 to 30% of the time, it could be cancer, which is what we refer to as the test’s positive predictive value.”
In current trials, “Galleri has shown a 62% accuracy in diagnosing cancer when it comes back positive,” Kaltman stated.
Conversely, a negative MCED result doesn’t rule out the possibility of cancer.
“It’s crucial for anyone who takes this test to continue regular screenings—colonoscopies, age-appropriate mammograms, and so on,” she advised.
Future studies will focus on the implications of test inaccuracies and whether MCED tests genuinely enhance patient longevity prior to FDA approval.
“False positives can lead to significant anxiety,” Kaltman mentioned.
For the FDA-sanctioned prostate cancer test, “We found many cancers that likely wouldn’t affect a person’s lifespan. Patients went through invasive surgeries unnecessarily, which they wouldn’t have needed if those cancers weren’t going to impact their longevity.”
Kaltman pointed out that current studies are examining how beneficial MCED tests are for prolonging lives.
“Are we catching the aggressive cancers early enough so that they can be treated effectively?” she pondered.
