Mutation detection using plasma circulating tumor DNA (ctDNA) in a cohort of asymptomatic adults at increased risk for cancer.

Purpose: The primary purpose of this study was to clinically evaluate circulating tumor DNA (ctDNA) with a nine gene, 96 mutation panel among subjects at increased risk for cancer with no previous cancer diagnosis.

Subjects and methods: DNA from 1059 asymptomatic subjects was analyzed for detection of low levels ctDNA using a blood plasma liquid biopsy assay. Subjects with detectable copies of ctDNA were asked to provide additional blood samples and relevant medical records throughout their one-year of participation. Subjects with a negative result were followed-up at one-year with a questionnaire.

Results: Mutations were detected in 58 subjects and not detected in 1001 subjects. Among the subjects who tested positive for one or more mutations, four were diagnosed with cancer, two of which through study-triggered clinical follow-up. Two subjects who tested negative on the screen received an early cancer diagnosis over the course of the year. The sensitivity of the assay at a threshold of ≥2 copies in this population was 66.67% and specificity was 94.87%. While the negative predictive value was 99.8%, the positive predictive value was only 6.9% in this cohort. Analysis of buffy coat DNA from eight positive subjects, including one who was diagnosed with cancer, revealed matching mutations suggesting that the ctDNA could have been derived from clonal hematopoiesis.

Conclusion: The observed false positive rate of ctDNA on a 96-mutation assay in an asymptomatic high-risk population is much greater than the true positive rate, limiting its usefulness as a cancer screening tool in its current form.