Relationship between genotoxic effects of breast cancer treatments and patient basal DNA integrity

It is accepted that radiotherapy and chemotherapy cause genotoxic effects as part of their therapy side effects, which are highly variable among different patients. This study evaluated DNA integrity using the comet assay in peripheral blood lymphocytes from breast cancer patients before (“pre-treatment patients”; n = 47) and after (“post-treatment patients”; n = 24) radiotherapy and/or chemotherapy treatment and from healthy donors (n = 15). Comet evaluation was made by visual (types 0-4) and digital (percentage of DNA remaining in the comet head = % head DNA) analysis. The association between the level of DNA damage and cancer prognostic factors was assessed. The treatments caused a significant increase in DNA damage registered by both visual (p < 0.001) and digital (p < 0.001) analysis. No significant associations between the level of DNA damage in pre-treatment patients and cancer prognostic factors were found. Results showed a significant correlation between the comet results from each patient before and after treatment (r = 0.64, p = 0.001). The % head DNA in post-treatment samples from patients with high level of DNA damage before treatment (30.3 ± 3.1%, p < 0.01) was lower than in post-treatment samples from patient with low to medium level of DNA damage before therapy (49.2 ± 4.4%). Results support the usefulness of the comet assay as a sensitive technique to evaluate the basal DNA status and the damage caused by cancer treatments. The assay could contribute to the treatment decisions, taking into account the patients’ basal DNA damage before therapy.