3401 - Circulating Tumor DNA Dynamics as Prognostic Biomarkers in Esophageal Squamous Cell Carcinoma (ESCC) Receiving Definitive Radiotherapy: A Prospective Cohort Study

Purpose/Objective(s): To observe the gene mutation characteristics of esophageal squamous cell carcinoma based on circulating tumor DNA (ctDNA), and screen biomarkers related to therapeutic efficacy.

Materials/Methods: This single-center, prospective cohort study consecutively enrolled 40 ESCC patients receiving curative radiotherapy and nimotuzumab (EGFR monoclonal antibody) systemic drug therapy at one institution from April 1, 2020, to January 31, 2022. We collected 7 tumor tissue samples and 71 plasma samples during treatment, using a customized 340-gene panel. Somatic mutations in tumor tissues and plasma samples were identified with next-generation sequencing and utilized for ctDNA-based MRD analysis.

Results: (1) Among Single Nucleotide Variations (SNV), TP53 and PIK3CA exhibited the highest mutation frequencies (45% and 12.5%, respectively), followed by NOTCH1/2, CDKN2A, CUL3, NFE2L2, and BRCA2 mutations (7.5%, 5%, 2.5%, 2.5%, and 2.5%, respectively). The most common type of copy-number variation (CNV) was the mutation in the 11q13.2-11q13.4 amp band (12.5%), corresponding to genes CCND1, FGF19, FGF4 and FGF3. The second most common types were EGFR and CDKN2A/CDKN2B mutations (both accounting for 5%). (2) The TP53 mutation rate in patients with cT4 stage was significantly higher than that in the cT2-3 group (60% vs. 20%, ?²=6.709, P=0.010). However, there was no significant correlation between pre-treatment driver gene mutation (including TP53 mutation) and patient’s PFS and OS. There was a significant difference in PFS between patients who remained TP53 mutation-positive after treatment and those who turned negative (95% CI 1.126-23.014, HR=5.090, P=0.035), of which 1-year, 2-year PFS rate were 50%, 33.3% and 83.3%, 75%, respectively. The OS of the two groups were statistically significant (95% CI 0.979-19.726, HR=4.394, P=0.053). (3) The ctDNA based minimal residual disease (MRD) positive rate was 18.8%. The 1- and 2-year PFS rates in the MRD(+) and MRD(-) groups were 50%, 33.3% and 76.9%, 65.2%(95% CI was 0.925-9.902, HR=3.027, P=0.067), respectively.(4)The detection rate of left shift (positive) of nucleosome positioning in the whole group before treatment was 55%, which decreased to 27.5% after treatment (?²=6.241,P=0.012).

Conclusion: TP53 was one of the most significant SNV-driven gene mutations in ESCC. Some patients’TP53 mutations could be eliminated through effective treatment. Patients with TP53 mutations positive before treatment and negative after treatment had a better prognosis than those with positive before and after treatment. The ctDNA-based MRD and nucleosome positioning were promising biomarkers worthy of further exploration.