One of the hottest topics at the 2026 American Society of Colon and Rectal Surgeons (ASCRS) Annual Scientific Meeting wasn’t a new operation—it was a blood test.
Specifically, surgeons were talking about circulating tumor DNA (ctDNA) and how it may change the way we monitor patients after colorectal cancer surgery.
At the same time, the American Cancer Society updated its colorectal cancer screening guidelines, expanding the role of blood-based screening tests for average-risk adults who decline or cannot complete traditional screening.
Not surprisingly, my patients immediately started asking the same question:
“Can I just get a blood test instead of a colonoscopy?”
The answer is yes… and no.
One of the biggest misconceptions is that all blood tests for colorectal cancer are the same. They’re not. There are actually two completely different blood tests serving two completely different purposes. The confusion tends to be– it’s all cTDNA, which means circulating tumor DNA. But for screening, we’re looking for cells before the tumor has been found. For molecular residual disease (MRD), we’re looking for cells after the tumor has been removed to guide chemotherapy options, such as in Stage II colon cancer. And in a third use case, we use cTDNA for surveillance to detect recurrence.
These are designed for people who have never been diagnosed with colorectal cancer. Their goal is simple- to detect cancer early.
The American Cancer Society now recognizes FDA-approved blood-based screening as an option for average-risk adults who are unwilling or unable to complete stool-based screening or colonoscopy.
This is exciting because increasing participation in screening will almost certainly save lives.
But remember! Blood-based screening detects cancer—it does not prevent it.
“Colonoscopy remains the gold standard for colorectal cancer screening.” — American Cancer Society 2026 guideline update
A colonoscopy remains the gold standard because it not only finds cancer, but also removes precancerous polyps before they become cancer.
ctDNA: Looking for Cancer After Treatment
ctDNA stands for circulating tumor DNA.
When cancer cells die, they release tiny fragments of DNA into the bloodstream. Highly sensitive laboratory tests can detect these fragments even when scans appear completely normal.
After surgery or chemotherapy, physicians use ctDNA to answer a very different question:
Is there microscopic cancer still hiding somewhere?
This is known as molecular residual disease (MRD).
Think of it this way:
A CT scan or colonoscopy looks for a visible fire.
ctDNA looks for smoke. And smoke can linger even after the fire has been put out. ctDNA testing can often identify recurrence months before a tumor becomes visible on CT imaging.
Although ASCRS 2026 included relatively few dedicated ctDNA presentations compared with ASCO, molecular residual disease was a recurring theme throughout colorectal cancer sessions.
One presentation examined molecular signatures associated with local recurrence after rectal cancer surgery, highlighting how genomic profiling and molecular biomarkers may eventually help identify patients at highest risk of recurrence before it becomes clinically apparent.
Another ASCRS presentation evaluated the accuracy of tumor-informed ctDNA assays for detecting molecular residual disease after colon cancer surgery, reflecting the growing interest among colorectal surgeons in incorporating liquid biopsy into postoperative surveillance.
The future of colorectal cancer surveillance is becoming increasingly personalized.
If you’re healthy and wondering about screening, don’t skip your colonoscopy because you heard about a blood test.
If you’ve already been diagnosed with colorectal cancer, ctDNA is an entirely different tool that helps your care team determine whether microscopic disease may still be present after treatment.
The future isn’t about replacing colonoscopy.
It’s about combining:
Better screening
Smarter surgery
Personalized cancer treatment
Molecular surveillance
Earlier detection of recurrence
Together, these advances are helping us diagnose cancer earlier, tailor treatment more precisely, and ultimately improve survival.
As we saw at ASCRS 2026, colorectal surgery is rapidly moving toward a future where treatment decisions are guided not only by what we can see on a scan, but also by what we can detect at the molecular level.
“The most effective screening test is the one the patient completes.” — American Cancer Society 2026 guideline update
Until next time, that’s just the way the anus wrinkles.
