Data from: Application of circulating tumor DNA as a non-invasive tool for monitoring the progression of colorectal cancer

Background: Liquid biopsy has been proposed to be a promising noninvasive
tool to obtain information on tumor progression. Through a clinical
observation of a case series of 6 consecutive patients, we aim to
determine the value of circulating tumor DNA (ctDNA) for monitoring the
tumor burden during the treatment of colorectal cancer (CRC). Materials
and methods: We used capture sequencing of 545 genes to identify somatic
alternations in primary tumor tissues of the six CRC patients who
underwent radical surgery and in 23 plasma samples collected at serial
time points. We compared the mutation patterns and variant allele
frequencies (VAFs) between the matched tissue and the plasma samples and
evaluated the potential advantage of using ctDNA as a better tumor load
indicator to detect disease relapse over carcinoembryonic antigen (CEA),
cancer antigen (CA) 19-9 and imaging studies. Results: We identified
low-frequency mutations with a mean VAF of 0.88% (corresponding to a mean
tumor burden of 0.20ng/mL) in the preoperative plasmas of four patients
with locally advanced CRC and a subset of mutations shared by their
primary tumors. The tumor loads appeared a sudden decrease upon surgery or
other adjuvant treatments and then generally maintained at low levels
(0.092ng/mL) until disease recurred. ctDNA increased by 13-fold when
disease relapsed in one patient while the CEA and CA 19-9 levels remained
normal. In this patient, all six somatic mutations identified in the
preoperative plasma were detected in the recrudescent plasma again, with
five mutations showing allele fraction increase. Conclusions: We described
a multi-time-point profile of ctDNA of CRC patients during the course of
comprehensive treatment and observed a correlation of ctDNA level with the
clinically evaluated tumor progression. This demonstrated a new strategy
by analyzing the heterogeneous ctDNA to evaluate and monitor the tumor
burden in the treatment and follow-up of CRC patients, with potentially
better potency than conventional biomarkers.