S2538
Radiobiology – Immuno-radiobiology
ESTRO 2026
Results: ENI-sparing resulted in significantly higher lymphocyte counts one week after the start of CRT compare to standard treatment (mean ± SD: 1578 ± 373/µl vs. 950 ± 352/µl, p<0.01). Starting ENI after the upfront boost negated this effect, with lymphocyte counts not differing between groups two weeks after the start of CRT (983 ± 0.390/µl vs. 1021 ± 611/µl, p=0.88; Figure 2A). Over the course of treatment, rates of grade 3 or grade 4 lymphopenia did not differ significantly between the ENI-sparing and the standard cohort. In total, 13 patients developed Grade 3 lymphopenia and 6 patients developed Grade 4 lymphopenia. 2 Patients did not develop any hematologic Grade ≥ 3 event (one in each arm). Median time to grade ≥ 3 lymphopenia was 34 days (95%-Confidence interval: 25 - 41 days). Initial ENI-sparing resulted in higher leukocyte counts throughout treatment, especially during weeks 4 - 6 (Figure2B). There were no occurrences of grade ≥ 3 thrombopenia in any patient.
Conclusion: ENI in HNSCC is associated with severe and early hematological alterations and ENI-associated lymphopenia is likely to be a contributing factor to the failure of several recent radioimmunotherapy trials. These exploratory clinical findings are in line with the biodosimetric results of this study, which are reported elsewhere. Results of this trial may guide the design of future radioimmunotherapy trials for HNSCC. Keywords: radiation-induced lymphopenia, radioimmunotherapy Pilot Study of Predictive Factors for Treatment- Related Lymphopenia in Locally Advanced Lung Cancer Ana González Morales 1 , Luz Rubí Olea 1 , Sergio López Rodríguez 1 , Nuria Naranjo Jiménez 2 , Elena Cenizo de Castro 2 , Salvador García Pareja 2 , José Abelardo Martín- Viera Cueto 2 , Jorge Contreros 1 1 Radiation Oncology, HRUM, Málaga, Spain. 2 Physics, HRUM, Málaga, Spain Purpose/Objective: Treatment-related lymphopenia, resulting from the radiolysis of circulating lymphocytes, suppresses antitumor immunity and correlates with poorer outcomes in locally advanced lung cancer (LALC). The Digital Poster 3487
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