Radiation-Induced Lymphocyte Apoptosis and Chromosomic Aberrations for Prediction of Toxicities in Patients Treated by Hypofractionated Radiotherapy for Breast or Prostate Cancers

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Abstract
Background: In trials using normofractionated regimen, the radiation-induced lymphocyte apoptosis (RILA) and the chromosomal damage assays (CDA) have shown prognostic roles of radiation-induced adverse events. The main objectives here were to validate RILA and CDA in extreme and moderate hypofractionation regimens for breast (FAST) and prostate (CHHiP) cancers. Methods: Blood samples were collected from 400 volunteers included in FAST and CHHiP trials. The primary endpoints (PE) were first change in photographic breast appearance and first grade ≥2 RTOG bladder or bowel toxicity (BBT) in FAST and CHHiP, respectively. The secondary endpoints was first grade ≥2 breast clinical changes (BCC) in FAST and BBT using different scales in CHHiP. Results: 103 FAST and 297 CHHiP patients with lab and clinical data were included. In FAST trial, no significant association of RILA with the primary endpoint was observed. A significant association of higher RILA levels with lower risk of any RIAE was found. The risk of developing grade ≥2 RIAE decreased significantly for patients with RILA≥24% compared to those with RILA≤16% with a HR of 0.50 (95%CI 0.25-1.00, p=0.012). Concerning chromosomic aberrations, no significant associations were found with change in photographic breast appearance nor with the secondary endpoint of any RIAE. In CHHiP trial, a decreased risk of grade≥2 RTOG bladder or bowel RIAE was observed for increasing values of RILA (HR 0.97, 95%CI 0.94-1.01, p=0.11) but did not reach statistical significance. Concerning chromosomic aberrations, we found significant association of higher levels of micronuclei per cell with lower risk of gr2+ RTOGAE (p=0.021 for trend test across tertiles; p=0.023 for upper vs lower tertile). Conclusions: This study is the first to evaluate RILA and CDA as predictors of late effects after breast and prostate RT in the “hypofractionation” era. Development of toxicity biomarkers whatever the RT fractionation are urgently needed.

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