DNA damage in peripheral lymphocytes of untreated breast cancer patients

Background

Using the alkaline comet assay, DNA single-strand breaks (ssb) have been described in peripheral blood lymphocytes (PBL) from breast cancer patients without treatment, but there is no information concerning the occurrence of double-strand breaks (dsb) in the same patients. The purpose of this study was to investigate whether PBL of untreated sporadic breast cancer patients harbor an elevated number of both DNA strand breaks.

Methods

Forty breast cancer patients without family history of cancer in clinical stage III devoid of treatment and 60 age-matched healthy subjects without history of breast cancer were included. PBL from freshly drawn blood were processed following two different methods: the alkaline and the neutral comet assay. Percentage and tail moment were assessed under fluorescence microscopy and a computer-based image analysis system.

Results

In controls, ssb were found in 18 ± 4.67% of PBL, and dsb at 7.99 ± 3.67% of PBLs. Cancer patients had higher values of both ssb 24.08 ± 4.96 (p <0.05) and dsb 13.11 ± 3.2% (p <0.01). Tail moment for ssb was 6.23 ± 1.44 and dsb, 2.31 ± 1.09 for controls. For breast cancer patients, tail moment for ssb was 11.73 ± 2.40 and for dsb, 6.33 ± 1.75 (p <0.01). On plotting individual measurements of comet percentage against tail moment for alkaline and neutral comet assays, clear separation of control group from cancer patients can be seen in both assays.

Conclusions

Demonstration of two types of DNA damage in PBL of breast cancer patients devoid of treatment or without exposure to environmental genotoxic agents provides a better picture of the degree of DNA damage present in somatic cells of these patients.

Key words: DNA single-stand breaks, Double-strand breaks, Breast cancer, Genomic instability, Sporadic breast cancer, Comet assay