Impacts of post-radiotherapy lymphocyte count onprogression-free and overall survival in patients with stage III lung cancer

Abstract

Background: We evaluated the impact of thoracic radiation in patients withnon-small cell lung cancer (NSCLC), considering the depletion of total lympho-cytes, use or not of chemotherapy, and radiation doses in healthy lung tissue.Methods: Patients with stage III NSCLC, ECOG 0 to 2, receiving radiothera pywith or without chemotherapy were prospectively evaluated. All patients shouldbe treated with three-dimensional radiotherapy and received biologically effectivedoses (BED10α/β 10) of 48 to 80 Gy. Peripheral blood lymphocyte total countswere measured at the start of radiotherapy and at 2, 6 and 12 months after radio-therapy. Along with lymphocytes, PTV and doses of 5 Gy and 20 Gy in healthylung tissue were also evaluated as potential factors inuencing overall survival(OS) and progression-free survival (PFS).Results: A total of 46 patients were prospectively evaluated from April 2016 toAugust 2019, with a median follow-up of 13 months (interquartile range, 1–39months). The median of OS of all cohort was 22,8 months (IC 95% 17,6–28,1)and the median PFS was 19,5 months (IC 95%: 14,7–24,2). Most patientsreceived concurrent or neoadjuvant chemotherapy (43; 93.4%). No patientreceived adjuvant immunotherapy. The lower the lymphocyte loss at 6 monthsafter radiotherapy (every 100 lymphocytes/mcL), the greater the chance of PFS(HR, 0.44; 95%CI, 0.25–0.77; P = 0.004) and OS (HR, 0.83; 95%CI, 0.70–0.98;P = 0.025; P = 0.025). BED was a protective factor for both PFS (HR, 0.52; 95%CI 0.33 –0.83; P = 0.0006) and OS (HR, 0.73; 95%CI 0.54–0.97; P = 0.029).Conclusions: Our results suggest that lymphocyte depletion after radiotherapyreduces tumor control and survival in patients with stage III lung cancer. Radia-tion doses equal or higher than 60 Gy (BED1072 Gy) improve PFS and OS, butthey negatively affect lymphocyte counts for months, which reduces survival andthe potential of immunotherapy.