S826
Clinical - Lung
ESTRO 2026
Digital Poster 3876
Impact of Lymphopenia on Treatment Outcomes in Limited-Stage Small Cell Lung Cancer treated with definitive chemo-radiotherapy Francesco Martucci 1 , Lisa Milan 2 , Antonio Angrisani 1 , Salvatore Cozzi 1 , Letizia Deantonio 1,3 , Thomas Zilli 1,3 1 Radiation Oncology Clinic, Ente Ospedaliero Cantonale (EOC) - Oncology Institute of Southern Switzerland (IOSI), Bellinzona, Switzerland. 2 Medical Physics Division, Ente Ospedaliero Cantonale (EOC) - Imaging Institute of Southern Switzerland (IIMSI), Bellinzona, Switzerland. 3 Facoltà Di Scienze Biomediche, Università Della Svizzera Italiana (USI), Lugano, Switzerland Purpose/Objective: Radiotherapy (RT) is essential in treating limited-stage small cell lung cancer (LS-SCLC), but it may induce lymphopenia, characterized by reduced lymphocyte count, potentially affecting treatment outcomes. This retrospective, mono-institutional study examines how lymphopenia and Effective Dose to Immune Cells (EDIC) impact overall survival (OS) and progression- free survival (PFS) in LS-SCLC patients. Material/Methods: We analyzed 50 LS-SCLC patients who received definitive chemo-radiotherapy at our institution between January 2010 and December 2019. RT was delivered using VMAT technique, with median dose of 54Gy (range: 40–60Gy). Forty-seven (94%) patients received concurrent or sequential cisplatin/etoposide. EDIC was calculated using the model by Jin and colleagues[1]. Blood samples collected at the end of RT determined lymphocyte counts. The primary endpoints were OS (time from diagnosis to death) and PFS (time from RT to first recurrence/metastasis). Quantitative variables were expressed as medians with interquartile ranges, and differences in categorical data were assessed using χ² test. Receiver- operating characteristic (ROC) analysis determined optimal cutoff points for OS and PFS. Cox proportional hazards models estimated hazard ratios (HRs) in univariable and multivariable analyses. Results: Median age was 67 years (range:47–83). Median EDIC and lymphocyte count at the end of RT were 2.23 Gy (range: 0.99–4.41) and 0.50 x 10^9/L (range: 0.03–1.13), respectively. Median OS and PFS were 31 months (range: 7–172) and 24 months (range: 4–172), respectively. Clinical features at presentation were not associated with OS or PFS, except for stage, which was related to both. Outcome was also associated with age (>61) and lymphocyte count ( ≤ 0.67 x 10^9/L), but not with PFS. Table 1 reports the optimal cutoff points by ROC analysis for PFS and OS. Male sex and stage > IIIA were significantly associated with worse PFS, while
Conclusion: SBRT provides a feasible and safe curative treatment approach for patients with early stage centrally and ultra-centrally located lung tumours, yielding convincing local control at moderate risk. 60 Gy in 8 fractions is a promising fractionation scheme, but we recommend prioritization of OAR constraints over PTV coverage, to mitigate fatal toxicities. References: 1. Bray, F. et al. Global cancer statistics 2022: GLOBOCAN estimates of incidence and mortality worldwide for 36 cancers in 185 countries. CA. Cancer J. (2024).2. Crabtree, T. D. et al. Stereotactic body radiation therapy versus surgical resection for stage I non–small cell lung cancer. J. Thorac. Cardiovasc. Surg. (2010).3. Timmerman, R. D. et al. Long-term Results of Stereotactic Body Radiation Therapy in Medically Inoperable Stage I Non–Small Cell Lung Cancer. JAMA Oncol. (2018).4. Palma, D. A. et al. Stereotactic Ablative Radiotherapy for the Comprehensive Treatment of Oligometastatic Cancers: Long-Term Results of the SABR-COMET Phase II Randomized Trial. J. Clin. Oncol. Off. J. Am. Soc. Clin. Oncol. (2020). Keywords: SBRT, NSCLC, meta-analysis
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