The micronucleus test in binucleated lymphocytes is a sensitive standard assay for biomonitoring, mutagenicity testing and to assess radiosensitivity of blood donors. The results vary between laboratories and scorers which led to the definition of international scoring criteria. We used these criteria in a case-control study, but nevertheless observed large differences between the seven scorers on the level of descriptive analysis. Therefore, we used the repeat measurements (267 in 98 blood donors) from this dataset (354 measurements in 185 blood donors) to analyse scoring variability in the setting of a case-control study. The variability was assessed by analysis of variance, which revealed the storage time of the blood samples, the blood donors including their disease status, and the scorers as sources of variation in the entire dataset. In addition, the coefficient of variation (CV) of the measurements was determined (overall: CV = 24.3%). After stepwise removal of biological and experimental variation by normalizations, the CV dropped to 6.8% on average, which may reflect the 'pure counting error'. The scorer-specific CVs were between 5.5 and 9.5%. The differences between the scorers suggested by the raw data were neither related to the scorer-specific CV nor to their experience. Instead, we observed a general decline of the micronuclei frequencies towards the end of the study for all scorers. This could not be related to a change in experimental conditions or in the defined scoring criteria. An explanation could be an unintended and unrecognized change of scoring criteria. Since the change in the results did not occur in automated counting we suggest to use either reference slides in longer-lasting studies or automated counting by image analysis.
The micronucleus test (MNT) has shown increased micronuclei (MN) frequencies in BRCA associated and sporadic breast cancer patients, Ataxia telangiectasia and Nijmegen Breakage Syndrome patients, demonstrating a common cellular phenotype of increased radiosensitivity. Some genes, causative of these diseases, have also recently been associated with prostate cancer. In order to investigate if prostate cancer exhibits the cellular phenotype of increased radiosensitivity, we performed MNT analysis on 22 sporadic prostate cancer patients and 43 male controls. We determined the baseline MN frequency, in order to see in vivo chromosomal damage without radiation, and induced (after irradiation with 2 Gy) frequency of MN, both in binucleated cells (BNC) obtained from cultured peripheral blood lymphocytes. An automated image analysis system was used to score the MN employing two different classifiers (Classifier A and B) for detection of BNC. The mean baseline frequencies were 48/43 MN/1000 BNC (A/B) for the controls and 42/50 (A/B) for prostate cancer patients. The induced MN frequencies amounted to 107/111 MN/1000 BNC (A/B) for controls and 111/114 MN/1000 BNC (A/B) for prostate cancer patients. The obtained MN frequencies did not result in a statistically significant difference between unselected cases and controls. However, restricting the analysis to young patients (50–60 years, N = 7) and age-matched controls (N = 7) revealed marginally significant higher MN frequencies in patients. We conclude that increased radiosensitivity is not a property of prostate cancer patients in general.
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