Background: The neoadjuvant chemotherapy plays an important role in the current treatment of colorectal cancer (CRC), even though parts of patients could not be benefit from it. This study was aimed to explore the specific mutational profile of plasma cell free DNA (cfDNA) in CRC patients with or without response to neoadjuvant chemotherapy. 

Methods: 16 eligible CRC patients were enrolled in this study from Harbin Medical University Cancer Hospital. These patients were divided into two groups: with response ( R, n = 8) and without response (NR, n = 8) to neoadjuvant chemotherapy. All patients received neoadjuvant chemotherapy and their baseline blood samples were collected. The cfDNA fragments were extracted for enrichment of a panel covering exon regions of 1,086 genes. Gene alterations were analyzed to investigate the relationship between genetic characterizations of cfDNA and response to neoadjuvant chemotherapy. 

Results: Principal component (PCA) analysis for copy number variation(CNV) of cfDNA differed significantly in two groups. In the R group, there were higher frequency CNV loss in ABL-1, ERBB3, SMO, IGF1R, AURKA, PDGFRA, IDH1, BRAF, PIK3CB, NRAS, NF1, MITF, PTCH1 genes, and CNV gain in MTRR, HSP90AA1, VHL, CREBBP, CHEK2, DDR2, MUTYH, NCOA1, XPC, FANCA genes. Regarding to the area under the ROC curve, CNV of these genes had a high value of 0.967, which implied that CNV of the candidate genes have predictive value for identifying response to neoadjuvant chemotherapy in CRC patients. Furthermore, the Copy Number Instability (CNI) value of R group was significantly higher than NR group(p = 0.0014). 

Conclusions: The candidate genes’ copy number variation and CNI value of baseline plasma cfDNA can identify the colorectal cancer patients with response or without response to neoadjuvant chemotherapy in this small cohort. The molecular profile of cfDNA in plasma may be a potential biomarker for predicting the response to neoadjuvant chemotherapy in colorectal cancer patients. These findings warrant further expanded prospective cohorts to validate.