Cell-free DNA (cfDNA) and circulating tumour DNA (ctDNA) are the small fragments released by tumour cells or healthy cells after the cell death process. These miniature fragments are released into blood circulation, and ctDNA is released by tumour cells, carrying cancer genetic alterations such as point mutations, methylation, or copy number variations. Nasrin Sarafan-Vasseur, Lead Scientist at the University of Rouen, Normandy, discussed the applicability of digital PCR and NGS in detecting molecular biomarkers in patients with solid tumours across three different cancer types: hepatocellular carcinoma, cervical cancer, and metastatic colorectal cancer.
Hepatocellular carcinoma (HCC) is the main subtype of all primary liver malignancy and transarterial chemoembolization (TACE) is the first line of treatment for intermediate-stage hepatocellular carcinoma. Sarafan-Vasseur explained that 70% of HCC patients secrete the alpha fetoprotein so the TACE procedure needs more label biomarkers for the assessment of the efficacy of this procedure.
So, they decided to conduct a pilot study involving 38 patients. Blood samples were collected from patients one day before the TACE procedure, two days after TACE, and one month after TACE. The objective was to evaluate the predictive impact of ctDNA on progressive disease. Results showed that cfDNA and ctDNA levels significantly increased after TACE, unlike alpha fetoprotein. Additionally, a scoring system combining cfDNA and ctDNA changes helped distinguish responders from non-responders and predicted progression-free survival.
Cervical cancer is the fourth most common cancer in women in terms of incidence and mortality mainly caused by Human Papilloma Virus (HPV). Several HPV subtypes are considered high-risk oncogenetic but subtypes 16 and 18 are the most frequent. Sarafan-Vasseur set up a multiplex assay for the detection of 91% of HPV genotypes in cervical cancer. A study on 97 patients showed that 59 patients were HPV-positive at baseline. More importantly, HPV circulating DNA is associated with node invasion, but the team didn't find any association between circulating HPV and disease-free survival at baseline.
Finally, the colorectal case study combined two cohorts with almost 200 patients and the patients were divided into two groups: patients treated with three drugs or more or patients treated with two drugs or less. Sarafan-Vasseur used a CRC panel that targeted CRC somatic mutations including KRAS and BRAF, the panel was validated with a sensitivity of 87%. Furthermore, they found good concordance between digital PCR and NGS. Overall, early changes in circulating tumour DNA were associated with treatment intensity and had a significant impact on prognosis.
Sarafan-Vasseur emphasised the fact that ctDNA and cfDNA are promising biomarkers for monitoring treatment efficacy. It is also vital that more prospective studies are carried out to confirm the findings from the pilot studies and retrospective analyses.
