93P - Circulating cell-free DNA fragmentation profiles during systemic therapy of advanced-stage non-small cell lung cancer patients

Background

Circulating cell-free DNA (cfDNA) may be used for monitoring response to systemic treatment in patients with advanced carcinomas. Tumor-derived cfDNA is characterized by a shift of fragment sizes. The aim of the study was to evaluate longitudinally the changes in cfDNA fragmentation profile and correlate it with disease progression in non-small cell lung cancer (NSCLC) patients receiving anticancer systemic therapy.

Methods

We recruited 14 patients aged 36 - 72 years at diagnosis with advanced stage IIIb/IV NSCLC and performance status 0-2 at diagnosis. All patients were initially tested on PD-L1 expression as well as on mutations in the EGFR and the ALK genes. Patients with positive PD-L1 expression (n=3) received immunotherapy pembrolizumab as the first-line therapy, those with mutations in the EGFR gene (n=3) received tyrosine kinase inhibitor - gefitinib, one ALK-positive patient received alectinib, while other patients received standard chemotherapy - Carboplatin/Etoposide (n=3) or Carboplatin/Paclitaxel (n=4). Consecutive plasma samples were collected at diagnosis, during systemic treatment and after termination of the therapy. cfDNA was extracted from 0.5 mL of plasma using magnetic-based MagMax cfDNA extraction kit, and quantified using Qubit HS dsDNA assay and ddPCR. Contamination with genomic DNA was determined using a B-cell-specific ddPCR assay. Fragment size distribution of cfDNA was determined by Agilent Bioanalyzer HS dsDNA assay.

Results

Concentrations of cfDNA measured by Qubit (∼14.3 ng/mL of plasma) showed good correlation to the absolute quantification determined by ddPCR (∼13.22 ng/mL of plasma). In a 38% of samples there was small contamination by peripheral blood cells gDNA. Besides expected fraction of cfDNA (168 bp mode) observed in all samples, we observed in 48% of samples an ultra-short fraction of cfDNA (50bp mode).

Conclusions

Application of magnetic-based cfDNA extraction method allowed us to detect an ultra-short cfDNA fraction, previously unrecognized in lung cancer patients. Studies to correlate it to progression-free survival are ongoing.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

Institute for Oncology and Radiology of Serbia.

Funding

The Science Fund of the Republic of Serbia (PROMIS/2020/6060876).

Disclosure

All authors have declared no conflicts of interest.