Objectives: There is growing evidence in many tumor types that circulating tumor DNA (cTDNA) can be predictive of recurrent cancer in high-risk patients. We present our early experience utilizing cTDNA surveillance in high-risk surgical oncology patients. cTDNA is performed by creating a signature profile using the 16 most prevalent genomic biomarkers from a patient’s tumor that had previously been biopsied or removed. The patient then has serial blood draws and utilizing the specific DNA markers a PCR assay is utilized to detect the presence of circulating tumor specific DNA.
Methods: A retrospective study was performed evaluating high-risk patients who had had serial cTDNA follow up. All patients had previously undergone surgical resection of their primary tumor or metastatic disease and were rendered surgically and radiographically disease free. Primary tumor cell blocks were utilized to develop PCR probes to detect cTDNA by Signatera. CTDNA specimens were obtained 1 month after surgery and then monthly. Clinical examination and high-risk screening were also performed per cancer guidelines.
Results: 39 patients were followed with cTDNA, 9 breast cancer, 16 colorectal,1 pancreatic and 13 melanomas. During follow up 7/39 patients developed positive cDNA, 2/7 were symptomatic at presentation. Of the 7 tests that were positive, 6 were found to have recurrent/metastatic disease by imaging. 1 patient had a positive test 1 month after surgery and the second follow up test was back to 0, they remained disease free. All patients with negative cDNA remain disease free on clinical and radiographic follow-up.
Conclusion: Testing for circulating DNA has been studied to assess for molecular residual disease after surgical resection as well as to help monitor treatment response in patients actively undergoing treatments for cancer. Our study evaluated the utility of cTDNA in a small group of high -risk patients. Elevated cTDNA was the first indicator of recurrence in 6 patients allowing for early detection and treatment. Patients with no evidence of cTDNA remain disease free. This small group of patients represent our ongoing evaluation of the utility of cTDNA to detect recurrent cancer allowing for additional therapy. Additional studies will need to be done utilizing larger volumes of patients; also assessing if this helps with survival outcomes and comparing if it is more cost effective to follow with cTDNA compared to the standard surveillance screening modalities.
