PNA-FISH-based Chromosome Aberration Frequency and Serum IL-6 as Predictive Biomarkers for Radiation Therapy-induced Pneumonitis in Lung Cancer Patients

Accurate prediction of symptomatic radiation therapy-induced pneumonitis (RT-IP) remains an important clinical challenge. Currently, mean lung dose and volume of the lungs receiving a 20 Gy threshold of ≤20 Gy and ≤35%, respectively, are utilized to reduce the incidence of pneumonitis to 20%. However, its occurrence is not entirely predictable even at the recommended threshold levels. Hence, in this study, we aimed to evaluate several biological markers, specifically chromosome aberrations by peptide nucleic acid fluorescence in situ hybridization (PNA-FISH), γH2AX, serum IL-6, and IL-17, as potential predictors of symptomatic (grade ≥2) radiation therapy-induced pneumonitis. We prospectively enrolled patients with locally advanced lung cancer. Peripheral blood samples were collected from eleven patients before, during (2 Gy, 20 Gy, 60/66 Gy), and one month after chemoradiotherapy. We then compared these biomarkers between overreactors (grade ≥2 RT-IP) and non-overreactors (grade 0 to 1 RT-IP). Our findings show that chromosome aberration frequency, serum IL-6, and IL-17 after 20 Gy are higher in overreactors than in non-overreactors. Moreover, overreactors accumulated more complex aberrations, such as tricentrics, quadricentrics, and quintacentrics. While chromosome aberration frequency correlated with mean lung dose and IL-17, a pneumonitis marker, IL-6 correlated with the irradiated volume after 20 Gy. Receiver operating characteristic curve analysis further showed that chromosome aberration frequency and IL-6 have the highest specificity for predicting grade ≥2 RT-IP among the assays. In conclusion, we demonstrated the superior predictive capability of PNA-FISH-based chromosome aberration frequency and serum IL-6 for radiation therapy-induced pneumonitis in lung cancer patients. This supports the usefulness of these biomarkers for predicting radiation therapy-induced pneumonitis.