Prognostic value of circulating tumor DNA (ctDNA) in metastatic colorectal cancer (mCRC) needs to be validated in prospective clinical studies using precise and robust procedures. In this context, picoliter-droplet digital PCR has arisen as a highly sensitive and quantitative approach offering a broad dynamic range of detection.
All consecutive mCRC patients receiving chemotherapy were included in this monocentric prospective study between October 2012 and April 2015. Plasma samples were collected before the first cycle of chemotherapy, then at 14 and 28 days. For each patient, tumor DNA from biopsies was tested for the presence of KRAS, BRAF and TP53 mutations either by conventional qPCR or Next-Generation Sequencing. When no mutation was identified in the tumor, ctDNA was screened for hypermethylated sequences of WIF1 and NPY genes. CtDNA sequences (mutated or hypermethylated) were quantified (concentration, ng/mL) using picoliter-droplet digital PCR coupled to Taqman probes. Impact of ctDNA on survival and tumor response (RECIST 1.1) was analyzed using the Cox model with adjustment on age, sex and Kohne score.
Overall, 113 patients were included. Preliminary results are focused on 70 mCRC patients treated with first-line chemotherapy (mean age: 65.7 yr [35.1-90.7]; male, 58.6%). The concentration of baseline ctDNA was significantly associated with a worse overall survival (OS) (first vs third tertile: HR= 4.77, CI95% [1.0-22.2]; p = 0.046). At 14 or 28 days, patients whom ctDNA concentrations remain above 0.2ng/mL have a significantly worse progression free survival (PFS) (HR 7.1, CI95% [2.3-21.9]; p = 0.001). Reduction in ctDNA level at 14 or 28 days under 0.2 ng/mL was significantly associated with CT tumor responses at 8 weeks (p
This study suggests that ctDNA is a significant prognostic factor in mCRC able to predict PFS and tumor response precociously. The quantifying circulating tumor DNA by picoliter-droplet digital PCR in mCRC appears to be relevant to tailor the treatment of mCRC.
Clinical trial identification
ClinicalTrials.gov Identifier: NCT01983098
Legal entity responsible for the study
A. Zaanan: Has participated in consulting or/and advisory boards for Roche, Merck Serono, Amgen, Sanofi and Lilly. J. Taieb: Has participated in consulting or/and advisory boards for Merck, Sanofi, Roche Genentech, Pfizer and Amgen. P. Laurent-Puig: Has participated in consulting or/and advisory boards for Sanofi, Merck Serono, Amgen, Roche, Genomic Health, Myriad Genetics and Pfizer. All other authors have declared no conflicts of interest.