Radiation-related lymphopenia after pelvic nodal irradiation for prostate cancer.

Abstract

26 Background: Given uncertainty regarding the effectiveness of pelvic nodal irradiation (PNI) for prostate cancer, we aimed to determine whether prostate cancer patients treated with PNI are at a higher risk of developing radiation-related lymphopenia (RRL) and whether RRL is predictive for worse treatment outcomes. Methods: The electronic charts of 886 consecutive patients treated with radiation therapy (RT) for prostate cancer from 2006 to 2018 at our institution were retrospectively analyzed. Qualifying patients were those with total lymphocyte counts (TLCs) within one year prior to and 3–24 months after the start of RT. Lymphopenia was the primary outcome; overall survival (OS) and biochemical progression-free survival (bPFS) were secondary outcomes. Results: Thirty-six patients with PNI and ninety-five patients without PNI qualified. In the PNI cohort, 61.1% of patients developed RRL (median follow-up TLC < 1000 cells/µL), versus 26.3% of non-PNI patients. On univariate analysis, initial prostate specific antigen (iPSA), baseline lymphopenia, treatment modality, PNI status, increased planned target volume, and androgen deprivation therapy administration were all significant predictors of RRL ( p < 0.05). On multivariate analysis, PNI status was a significant predictor of RRL ( p < 0.001; HR 3.42; 95% CI 1.22–9.61) as well as iPSA ( p = 0.006; HR 1.05; 95% CI 1.00–1.11) and baseline lymphopenia ( p = 0.007; HR 8.32; 95% CI 2.19–31.6). RRL was not predictive for bPFS, distant metastasis, or OS on multivariate analysis, though the numbers of events were likely insufficient for these analyses. Conclusions: The higher risk of RRL among PNI patients comports with other papers that show increased treatment volumes are associated with higher rates of RRL. Mounting evidence for the adverse effects of RRL on clinical outcomes supports the significance of our findings and suggests further studies are needed on RRL as a potential harm of PNI that may affect interpretation of results from clinical trials of PNI.