Oral 55 – Clinical Application of Circulating Tumor DNA in Gastrointestinal Cancer Patients
Wednesday, October 26, 2022 | 8:30 AM – 8:40 AM ET | Location: Hall C2
Author Insight from Apaar Dadlani, MBBS, University of Louisville
What’s new here and important for clinicians?
ctDNA is a blood-based assay that can detect tumor DNA in circulation and thus identify even a microscopic cancer that would not be found by other conventional modalities like endoscopy or radiographic imaging. Conversely, absence of detectable ctDNA may imply absence of malignant cells in that patient.
We report a single center experience with using this technology to follow the disease status of patients with GI cancers. ctDNA was helpful in patients with metastatic colon cancer who had no detectable disease on CT scans after several rounds of treatment, who wanted to stop treatment but were anxious that conventional scans may not be picking up residual microscopic disease which could result in a recurrence after stopping treatment. A negative (undetectable) ctDNA provided a greater level of confidence and all the patients who stopped treatment based on this have not had a recurrence for over a year. In addition, ctDNA testing was helpful in selecting out certain frail or ill patients from having to take adjuvant chemotherapy after surgery for stage III colon cancer. Finally, this assay also correlated correctly with pathologic CR in a patient with rectal cancer who had neoadjuvant chemotherapy and radiation. If this predictivity proves to be strong, such patients may be spared from surgery and could be followed with close observation with a greater degree of confidence than one can get with imaging and endoscopy alone. While ctDNA appears to be highly predictive, more data with larger studies are needed to better understand the sensitivity and specificity of this assay. In our limited experience, there was a false negative rate of about 9%.
What do patients need to know?
ctDNA is a blood test that may be able to detect the presence or absence of a specific cancer at the molecular level unlike scans or endoscopies that can only find cancers that are visible to the naked eye.
This granularity can be helpful in making certain management decisions such as whether treatment can be safely stopped if no cancer is detectable on scans or whether chemotherapy after surgery may or may not be safe to withhold in patients who may be at very high risk of toxicities. We report successful use of ctDNA in both these scenarios in patients at our center. In addition, our study also included a patient with rectal cancer who got chemotherapy and radiation before surgery, and this patient’s initially detectable ctDNA became undetectable after this treatment. When this patient’s rectum was removed by surgery, no residual cancer was found in the specimen after detailed microscopic exam. If the test proves to have a high level of response prediction in larger studies, such patients may be able to avoid surgery altogether in the future.
While the ctDNA test appears to be strongly predictive of cancer status, it is not perfect and larger studies will be needed to see how sensitive it really is in predicting presence or absence of cancer. In our small study, the false negative rate was about 9%. In other words, out of a 100 patients with a negative (undetectable) ctDNA test (implying absence of cancer), 9 may have cancer that the test failed to detect.
Author Contact
Apaar Dadlani, MBBS, University of Louisville
apaar27 [at] gmail.com
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