ESTRO meets Asia 2024 Congress Report

We presented a talk on our findings that circulating tumour DNA (ctDNA) combined with PET standard uptake value (SUV) maximum values is a better predictive marker of recurrence after radiotherapy for early-stage lung adenocarcinoma than those previously used. The study was intended to explore a more helpful risk stratification method that combined ctDNA with other predictive factors. Thirty-eight patients who had been diagnosed with cT1-2N0M0 lung adenocarcinoma and treated with proton beam therapy at a single institution between January 2014 and December 2019 were enrolled in the study. The following factors, which have been previously reported, were chosen for study: gross tumour volume (GTV), consolidation to maximum tumour diameter ratio (CTR), PET SUV max, and carcinoembryonic antigen (CEA) value. At the median follow-up of 58 months, detectable ctDNA and SUV max of > 5 was associated with inferior progression-free survival (PFS) (hazard ratio [HR], 5.1; 95% CI, 1.8-14.7; and HR, 3.0; 95% CI, 1.2-7.8 respectively). No significant differences were observed in GTV, CTR, or CEA values. We created two risk groups: low risk, which comprised patients with undetectable ctDNA and low SUV max; and high risk, which comprised patients with either detectable ctDNA or high SUV max. Patients in the high risk group had significantly worse PFS than those in the low risk group (HR, 8.7; 95% CI, 2.5-30.2). The concordance (C)-index was 0.65 for ctDNA only and improved to 0.75 when SUVs were included.

The results of this study suggested that the combination of pre-treatment ctDNA and PET-CT SUV max was a better risk stratification method by which to predict the recurrence of early-stage lung adenocarcinoma that had been treated with radiotherapy. This risk stratification method, which combines ctDNA and PET, may help in the selection of patients for additional systemic therapy from among radiotherapy patients with early-stage lung adenocarcinoma. Future research is necessary to validate the results in a large-scale prospective study if this method is to be established as a predictive biomarker for recurrence of early-stage lung cancer after radiotherapy.

Masaki Nakamura

Department of Radiation Oncology, National Cancer Centre Hospital East, Chiba, Japan