Declared cancer-free: Weighing the pros and cons of a ctDNA test

Im a Mayo Rochester patient and I do the Natera By Signatera blood test every 2 months. I'm 3 years out from head and neck cancer so my scans are 6 months apart now. I find the Natera test reassuring. And one way to catch any recurring cancer early.

@sandy8043 Has your medical provider shared the reliability of the Signatera test? I’m also wondering about the reliability of ctDNA? False positives? False negatives? Science is moving ahead so quickly that I’m relieved but it’s hard to keep up with it all.

The ctDNA test my oncologist has suggested is called Guardant. Not sure how this compares with Signatera?

I was diagnosed with high-grade muscle invasive bladder cancer in the fall of 2023. At the time I had a large tumor in my bladder and while it showed on a CAT scan, it did not show that it was outside of the bladder yet. A sample of the tumor was taken for the test during the TRBT, but because of the size and condition of my bladder, a radical cystectomy was the only option. Fast-forward to January 2024 after my radical cystectomy and pathology of my lymph nodes, the cancer had in fact advanced beyond the bladder wall, but that never showed on scans. Chemo was successful for me and monitored by Signatera every three months. Unfotunately , after a year, the cancer began to return in my lymph node. It again did not show on CAT scans but was picked up by traces of the cancer DNA in my blood and then confirmed by PET scan. I am so grateful that this test gave me probably a six month lead on treatment that has again worked successfully for almost a year. While I know the scans are necessary, they unfortunately do not provide as much reassurance as the Signatera test does for me.

Hi, I am a 64 year old breast cancer survivor and was diagnosed with an aggressive type of endometrial cancer (serous p53 abn) in 2025. Due to major toxicities, I was only able to complete 2 rounds of the 6 rounds of chemo prescribed after surgery. One of my 2 oncologists recommended the Signatera test to check for possible recurrence. I’ve had 7 tests so far—5 negatives and 2 low positive results. I find the test to be reassuring and an important part of my care plan. Good luck and enjoy the ski season!

@naturegirl5 I know we discussed it at the onset...Oct. 2023.

@sandy8043 What did your medical provider tell you in your discussions?

@sandy8043 I have been asking my oncologist about the ctDNA and they have yet to test me with it instead wanting to rely on CT scans every three months. Their reason is they don’t know what to do with the information when they get it. Any good arguments I could throw at them? I have stage 4 colon cancer and been on a 6 month break but now they see something in my anal canal and don’t know if it’s cancer or just something left in there. I think the ctDNA would have lent a hand in determining if there was something to worry about. Now I have to wait for a colonoscopy.

Yes, my oncologist has said much the same but I'm encouraged by your comments and some of the other replies to my post. I think I would rather know if there are microscopic bits floating around that could get larger than not know. But I appreciate that this might increase anxiety for some people. Still not sure if the ctDNA test will take place but in the meantime I have another colonoscopy to look forward to! My oncologist said that a colonoscopy is a very useful tool for spotting things that a CT scan might not pick up.

I think the value of a blood biopsy depends upon the type of cancer and treatment options available. My oncologists have said that they wouldn’t know what to do with positive results if they didn’t know where the recurrence is. I now understand that this is because my rare endometrial cancer did not respond to chemo and there are no drugs that have been shown to work with my biomarkers. So if non-drug treatment is my only option and a CT scan doesn’t show anything, where would they operate or radiate?
Good luck with your colonoscopy. I find the prep terrible, but I give you this thought: there’s photo imaging of your insides that is not attainable in any other area of the body except for endoscopy. Wishing you clear photos!