New research led by the University of Leicester suggests it may be possible to reduce toxicity associated with breast cancer radiotherapy by identifying gene variants that affect circadian rhythm, and scheduling for morning or afternoon radiotherapy based on genetic profile.
The study examined the effect of radiotherapy timing in 2 breast cancer patient cohorts. The retrospective LeND study cohort comprised 535 patients scored for late effects using the Late Effects of Normal Tissue-Subjective Objective Management Analytical scale. Acute effects were assessed prospectively in 343 patients from the REQUITE study. Genotyping was carried out for candidate circadian rhythm variants.
The data showed that in the LeND cohort, patients who had radiotherapy in the morning had a significantly increased incidence of late toxicity in univariate (P=.03) and multivariate analysis (P=.01). Acute effects in the REQUITE group were also significantly increased in univariate analysis after morning treatment (P=.03) but not on multivariate analysis.
Increased late effects in the LeND group receiving morning radiotherapy were associated with carriage of the distinct genetic variants - PER3 variable number tandem repeat 4/4 genotype (P=.006) and the NOCT rs131116075 AA genotype (P=.005).
The study is published in Clinical Oncology, the journal of the Royal College of Radiologists.