Increased Sensitivity to Ionizing Radiation in a Relevant Subset of Patients with Cancer and Systemic Lupus Erythematosus

It has long been hypothesized that systemic lupus erythematosus (SLE) increases radiosensitivity, but recent studies have yielded mixed results. We studied individual radiosensitivity in 70 individuals with SLE using chromosomal aberrations as biomarkers of radiosensitivity. In total, 33 patients with SLE and 37 patients with SLE and additional oncologic diseases were compared with healthy individuals and with patients with rectal and breast cancer. Individual radiosensitivity was assessed by ex vivo irradiation of G0 blood lymphocytes followed by three-color fluorescence in situ hybridization of chromosomes 1, 2, and 4. SLE patients have slightly higher background rates of chromosomal aberrations than healthy individuals and lower rates than cancer patients. Non-oncologic SLE patients show a rate of chromosomal aberrations similar to that seen in healthy individuals. The outliers in this group, who clearly show increased radiosensitivity, fall between healthy individuals and cancer patients. Patients with SLE and cancer have significantly higher chromosome aberration rates compared to healthy individuals (<i>p</i> < 0.001) and patients with isolated cancer (<i>p</i> = 0.007) or isolated SLE (<i>p</i> = 0.004). The proportion of radiosensitive patients in the oncologic SLE cohort is high, with 45% of patients showing increased radiosensitivity. There is a weak association between anti-Ro-52 autoantibodies and radiosensitivity. Based on the radiosensitivity measurement, radiation dose reduction was recommended in 11 oncological SLE patients and was successfully achieved in 5 patients by up to 21% of the dose per fraction. In the oncologic SLE cohort, a substantial portion of individuals show increased radiosensitivity.