DNA double-strand break (DSB) repair analysis in epithelial mesenchymal transition cells (EMTs) derived from breast cancer specimens identifies new prognostic markers

Background: All currently known breast cancer susceptibility genes are linked to DSB repair. To find novel markers for breast cancer risk, we analyzed DSB repair in peripheral blood lymphocytes (PBLs) from high-risk individuals and revealed highly significant increases of error-prone mechanisms such as non-homologous end joining (NHEJ). To additionally capture non-hereditary factors as potential prognostic markers, we established a new primary cell model resembling breast cancer specimens and scrutinized DSB repair.

Material and methods: We developed a protocol for isolation and ex vivo analysis of epithelial cells, EMTs and fibroblasts from fresh breast cancer tissue (148 patients). Using a fluorescence-based test system for detection of distinct mechanisms we analysed DSB repair in these cell types and PBLs. In parallel we investigated DNA lesion processing by quantitative immunofluorescence microscopy of nuclear signals after radiomimetic treatment. Data for each variable were correlated with clinically relevant parameters.

Results and discussion: Our study reveals a gradual decline of repair capacity but not quality in epithelial cells from patients with increasing age. This pattern was strikingly different from EMTs and PBLs, where the group of young, mostly high-risk patients shows the lowest repair capacity and lowest repair quality, respectively. Most interestingly, we found elevated error-prone NHEJ in EMTs from patients with recommendation of adjuvant chemotherapy.

Conclusion: We carved out differences between hereditary and acquired DSB repair characteristics in breast cancer patients, which could be useful to predict responsiveness to targeted therapies and may serve as novel prognostic marker regarding the response to adjuvant chemotherapy.