Relationship between in vitro chromosomal radiosensitivity of peripheral blood lymphocytes and the expression of normal tissue damage following radiotherapy for breast cancer

Background and purpose: There is a need for rapid and reliable tests for the prediction of normal tissue responses to radiotherapy, as this could lead to individualization of patient radiotherapy schedules and thus improvements in the therapeutic ratio. Because the use of cultured fibroblasts is too slow to be practicable in a clinical setting, we evaluated the predictive role of assays of lymphocyte chromosomal radiosensitivity in patients having radiotherapy for breast cancer.Materials and methods: Radiosensitivity was assessed using a micronucleus (MN) assay at high dose rate (HDR) and low dose rate (LDR) on lymphocytes irradiated in the G₀ phase of the cell cycle (Scott D, Barber JB, Levine EL, Burril W, Roberts SA. Radiation-induced micronucleus induction in lymphocytes identifies a frequency of radiosensitive cases among breast cancer patients: a test for predispostion? Br. J. Cancer 1998;77;614-620) and an assay of G₂ phase chromatid radiosensitivity ('G₂ assay') (Scott D, Spreadborough A, Levine E, Roberts SA. Genetic predisposition in breast cancer. Lancet 1994; 344: 1444). In a study of acute reactions, blood samples were taken from breast cancer patients before the start of radiotherapy, and the skin reaction documented. 116 patients were tested with the HDR MN assay, 73 with the LDR MN assay and 123 with the G₂ assay. In a study of late reactions, samples were taken from a series of breast cancer patients 8-14 years after radiotherapy and the patients assessed for the severity of late effects according to the'LENT SOMA' scales. 47 were tested with the HDR assay, 26 with the LDR assay and 19 with the G₂ assay. For each clinical endpoint, patients were classified as being normal reactors or 'highly radiosensitive patients' (HR patients (Burnet NG. Johansen J, Turesson I, Nyman J. Describing patients' normal tissue reactions: Concerning the possiblity of individualising radiotherapy dose presciptions based on potential predictive assays of normal tissue radiosensitivity. Int. J. Cancer 1998;79:606-613)).Results: The HR patients could be identified in some of the assays. For example, for acute skin reactions, 9/123 patients were judged as HR; they had significantly higher G₂ scores than normal reactors (P=0.004). For the late reactions, the mean HDR MN scores were higher for the 4/47 patients who had severe telangiectasia (P=0.042) and the 8/47 patients had severe fibrosis (P=0.055). However, there were no trends towards increased chromosomal radiosensitivity with the micronucleus scores at HDR or LDR, or with G₂ chromosomal radiosensitivity.Conclusions: While these results support the concept of using lymphocytes to detect elevated sensitivity to radiotherapy (as an alternative to fibroblasts), these assays are unlikely to be of assistance for the prediction of normal tissue effects in the clinic in their present form. Copyright (C) 2000 Elsevier Science Ireland Ltd.