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715 Background: Lymphocyte-to-monocyte ratio (LMR) is a strong prognostic factor in many cancers. Recently, in Polish-2 study it was demonstrated to have a predictive value for hypofractionated neoadjuvant radiotherapy in rectal cancer (WCGIC 2017). LMR > 2.6 was associated with significant improvement of overall survival after short-course radiotherapy (5x5 Gy) and consolidating chemotherapy when compared to chemoradiotherapy (HR 0.36). To our knowledge this is the first observation on use of a predictive biomarker for hypofractionated radiotherapy. In this study we assessed the intra-patient variability of pre-treatment LMR in order to evaluate its reproducibility. Methods: Patients with rectal cancer treated in Maria Sklodowska-Curie Memorial Cancer Center, Warsaw, Poland between January 2013 and August 2017 were identified. In order to test reproducibility of the biomarker, only the patients with minimum two peripheral blood morphology tests within 5 weeks prior to any anti-cancer therapy were selected. Other inclusion criteria were locally advanced rectal cancer with no distant metastasis; no prior radiotherapy or chemotherapy. Patients with LMR > 2.6 were identified as “LMR high”. Results: After pre-screening of 719 rectal cancer patients, 50 patients met the inclusion criteria. LMRs calculated at two time-points were correlated with the coefficient of 0.588 (p < 0.05). 40% of assessments were “LMR high”. In 18% of patients the second test has not confirmed initial assignment to LMR class (95% CI 8.6%-31.4%). If LMR at the first time-point was in the range of 2.2-3.0 (+/- 0.4 from cut off), the chance for misclassification rose to 40% (95% CI 12.2%-73.8%), while outside of this range it dropped to 7.5% (95% CI 1.6%-20.4%). Conclusions: In our study LMR demonstrated significant intra-patient variability, espetially in patients with LMR outside of the indicated range (2.2-3.0). Further translational research is needed to identify the exact biological context of this biomarker in order to identify the molecular subtype of rectal cancer responding to hypofractionated radiotherapy.

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