In vitro chromosomal radiosensitivity in breast cancer patients

In vitro chromosomal radiosensitivity has been investigated in patients with inherited cancer prone syndromes (e.g. Ataxia Telangiectasia, Nijmegen breakage syndrome) and also in different types of cancer patients (e.g. head and neck-, colorectal cancer, breast cancer). In breast cancer patients enhanced chromosomal radiosensitivity is observed in several independent studies. In most of these studies chromosomal radiosensitivity was analysed by using the G2 and G0-MN assay for peripheral blood lymphocytes and it has been suggested that enhanced chromosomal radiosensitivity of PBL may be a marker for breast cancer predisposing genes of low penetrance. In the first part of this thesis we investigated the suitability of the G2 and G0-MN assay as biomarkers of individual radiosensitivity. Therefore we analysed the reproducibility and sensitivity of these assays. Our studies showed that the intra-individual variability of both assays is high and not different from the inter-individual variability. Although it was suggested in literature that the inter-individual variability might be attributable to the hormonal status in females, we could not demonstrate any influence of the blood serum levels of estradiol or progesterone on the intra-individual and inter-individual variability obtained in the G0-MN assay. In most of the studies investigating the in vitro chromosomal radiosensitivity of breast cancer patients the G0-MN assay has been performed on fresh blood cultures. Because the use of fresh blood cultures allows no repeated testing, we have investigated the suitability of EBVtransformed cell lines and IL-2 cultures for the analysis of chromosomal radiosensitivity in breast cancer patients. As we were not able to demonstrate the radiosensitive response in the cell cultures derived from the original PBL, care has to be taken when EBV-transformed cell lines or IL-2 cultures are used to assess chromosomal radiosensitivity in breast cancer patients.In the second part of this thesis, we analysed chromosomal radiosensitivity of different breast cancer populations with the G2 and G0-MN assay. We have demonstrated that a group of breast cancer patients with a known or putative genetic predisposition is more radiosensitive than a group of healthy women and this as well with the G2 and G0-MN assay. We showed that this enhanced in vitro chromosomal radiosensitivity is not correlated with the age of onset of the disease in breast cancer patients and that the enhanced chromosomal radiosensitivity in breast cancer patients with a mutation in BRCA1 or BRCA2 is not due to the presence of a mutation in these two genes. Analysis of the in vitro chromosomal radiosensitivity of a small group of breast cancer patients with a CHEK2 1100delC mutation revealed no correlation between the CHEK2 1100delC variant and chromosomal radiosensitivity. No correlation is found between the G2 and G0 chromosomal radiosensitivity, pointing to the fact that these two assays reflect different underlying mechanisms of chromosomal radiosensitivity. In conclusion, we performed a thorough analysis of the suitability of the G2 and G0-MN assay as biomarkers of individual radiosensitivity and we applied these assays to determine the chromosomal radiosensitivity of different population groups of breast cancer patients. We can conclude that both assays are very valuable to analyse chromosomal radiosensitivity in breast cancer populations. Further studies have to be performed to analyse the underlying mechanisms of chromosomal radiosensitivity