Change in the serum selenium level of patients with non-metastatic and metastatic non-small cell lung cancer (NSCLC) during radiotherapy as a predictive factor for survival

Background: Lung cancer remains a serious medical problem. The trace element selenium seems to be a promising prognostic marker or therapeutic option for cancer patients. Methods: We enrolled 99 patients with histologically confirmed NSCLC undergoing radiotherapy. The serum selenium level of these patients was determined prior to irradiation (t0), after reaching 20 Gy (t1), and at the end of radiotherapy (t2). Selenium concentrations were measured with total-reflection X‑ray fluorescence (TXRF) spectroscopy. We formed three subgroups according to the change in serum selenium levels across timepoints, and Kaplan–Meier analysis was used to estimate overall survival (OS). Further subgroups were patients with/without metastatic disease. We used adjusted Cox regression models. Results: The change in selenium concentration was especially significant between t0 and t1 for the whole study group (hazard ratio [HR] = 0.5, p = 0.03) as well as in patients with metastasized NSCLC (HR = 0.3, p = 0.04) after adjustment. The baseline selenium value in patients with non-metastasized NSCLC was associated with overall survival (HR = 0.3, p = 0.04). The change in selenium levels between t0 and t2 was significant in patients with metastatic lung cancer (HR = 0.1, p = 0.03). Patients with increased serum selenium levels during radiotherapy between the start of treatment (t0) and t1 had better OS (HR = 0.46, p = 0.05). Conclusion: Especially patients with increasing selenium levels during radiotherapy showed an improved overall survival. Thus, serum selenium might be a predictive factor for OS in NSCLC patients. The value of supplementation of the trace element is subject to future research.