BIOM-92. MONOCYTE-LYMPHOCYTE IMMUNODYNAMICS PROGNOSTICATE SURVIVAL IN GBM PATIENTS TREATED WITH CHEMORADIATION

Abstract PURPOSE/OBJECTIVE Lymphopenia has been associated with diminished survival in patients with glioblastoma (GBM). The effect of radiation on myeloid-derived suppressor cells and other immunosuppressive monocyte subpopulations may contribute to the persistence and severity of lympho-depletion. We aim to characterize how the interplay between monocytes and lymphocytes relates to overall survival in this cohort. MATERIALS/METHODS We retrospectively reviewed patients with GBM treated with concurrent chemotherapy and conventionally fractioned RT (chemoRT) between 2010 to 2020. For inclusion in our cohort, patients needed to have lymphocyte and monocyte counts during the following time periods: the two weeks before chemoRT, the two weeks after chemoRT, and within six-to-twelve weeks after chemoRT. We recorded patients’ clinical characteristics and treatment outcomes. Our main endpoint was overall survival, defined as time from starting chemoRT. Paired t-test was used to compare lymphocyte and monocyte counts at different time periods. Associations between key clinical characteristics with survival were assessed with Cox proportional hazard ratio (HR) models. RESULTS A total of 314 patients were included in our study. The median age was 59 years (range 21-85). Both absolute monocytes and lymphocytes decreased by mean of 0.13 (p<0.001) and.72 (p<0.001), respectively, during the RT course. Although there was some recovery of these cell counts by the 6-to-12-week period after RT, they remained lower than baseline values. There was a significant increase in monocyte lymphocyte ratio (MLR) from chemoRT initiation to completion (0.50 to 0.74, p<0.001), which also did not return to baseline by the 6-to-12-week period after chemoRT. On both univariate and multivariable analysis, MLR > 0.5 at 6-to-12-week period was prognostic for overall survival (HR: 1.5, 95% CI: 1.1 – 2.0). CONCLUSION We found that lymphocytes declined greater than monocytes during chemoRT. Elevated MLR in the 6-to-12-week period after completing chemoRT is associated with worse survival. This warrants further investigation.