J. He1, Y. Liu1, B. Li2, J. Yu2, and L. Wang2; 1Department of Radiation Oncology, Shandong Cancer Hospital and Institute, Shandong University, Jinan, China, 2Department of Radiation Oncology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, China
Purpose/Objective(s): Lymphopenia (RIL) is a known significant factor for treatment outcome in lung cancer patients, especially the one who undergoing immunotherapy. Thoracic radiation is frequently used for advanced non-small-cell lung cancer (NSCLC), and it has been utilized in radical treatments besides palliative therapy. We hypothesize that the estimated lymphocyte counts (EDRIC) are related with RIL in stage-IV lung cancer receiving immunotherapy and radiotherapy. Materials/
Methods: We conducted a retrospective analysis of 152 patients with stage IV NSCLC who had received first-line immunotherapy and thoracic radiation therapy. Clinical factors were extracted from the medical records. Peripheral lymphocyte counts (PLC) were collected during, before and after radiotherapy. We defined the lowest PLC during radiotherapy for determination of RIL. RIL was graded by Common Terminology Criteria for Adverse Events (CTCAE) version 4.0. Grade 1, 2 ,3 and 4 RILwere defined as PLC cut-off of 1.10-0.8*109,0.8-0.5*109,0.5-0.2*109 and 0.2*109 respectively. Spearman’s rank correlation was used to assess the correlation between lymphocyte and EDRIC. The association of EDRIC (<5.7Gy vs =5.7Gy) with overall survival (OS) and progression-free survival (PFS) were evaluated by Kaplan-Meier and Cox proportional methods. Results: Before radiotherapy, 29.6% patients had RIL. During radiotherapy, 84.9% patients had RIL, and the median PLC during radiation was 0.69*109/L. The cumulative prevalence of G1, G2, G3, and G4 RIL during radiotherapy were 20.4%, 27%, 30.3% and 7.2%, respectively. There is no significant relationship had been found for survival with the number of lymphocytes before or after radiotherapy. Negative correlations of EDRIC with lymphocyte nadir (r =-0.3172, Y = -0.0005854*X + 0.94, R2=0.101, p < 0.0001) was found. PFS and OS among different grade RIL had significant differences with P=0.001 and P=0.008, respectively. EDRIC was the only factor associated with worse PFS (HR=1.001, p = 0.018) and OS (HR=1.002, p = 0.001) in multivariate analysis. Median PFS and OS was shorter in the EDRIC =5.7Gy group (PFS: 10.2months vs 18.6months, p< 0.0001; OS: 19.8 months vs 30.2months, p=0.024). Conclusion: EDRIC is a significant factor for RIL among patients with stage-IV lung cancer undergoing thoracic radiation during the era of immunotherapy. EDRIC can potentially function as a predictor for lymphocyte nadir and offers a basis for the prospective evaluation of treatment strategies involving immunotherapy and radiation that could minimize the impact on lymphocytes.
