***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: The frequency of  micronuclei ( MN )  in peripheral blood lymphocytes ( PBL ) is extensively used as a biomarker of chromosomal damage and genome stability in human population s. Much theoretical evidence has been accumulated supporting the causal role of MN induction in cancer development , although prospect i ve cohort studies are needed to vali date MN as a cancer risk biomarker . A total of 6718 subjects from of 10 countries , screened in 20 laboratories for MN frequency between 1980 and 2002 in ad hoc studies or routine cytogenetic surveillance , were selected from the data base of the HUman MicroNucleus ( HUMN ) international collaborative project and followed up for cancer incidence or mortality . To st and ardize for the inter-laboratory variability subjects were classified according to the percentiles of  MN  distribution within each laboratory as low , medium or high frequency . A significant increase of all cancers incidence was found for subjects in the groups with medium ( RR=1.84 ; 95 % CI : 1.28 - 2.66 ) and high MN frequency ( RR=1.53 ; 1.04 - 2.25 ) . The same groups also showed a decreased cancer-free survival , i.e. P=0.001 and P=0.025 , respectively . This association was present in all national cohorts and for all major cancer sites , especially urogenital ( RR=2.80 ; 1.17 - 6.73 ) and gastro-intestinal cancers ( RR=1.74 ; 1.01 - 4.71 ) . The results from the present study provide preliminary evidence that MN frequency in PBL is a predictive biomarker of cancer risk within a population of healthy subjects . The current wide-spread use of the MN assay provides a valuable opportunity to apply this assay in the planning and validation of cancer surveillance and prevention programs The single-cell gel ( SCG ) test was used to study the induction and persistence of DNA damage by cyclophosphamide ( CP ) in human blood cells after treatment in vitro and in vivo . S9-mix-activated CP ( from 0.1 mM upward ) induced DNA effects in a concentration-dependent manner in the in-vitro SCG test . Blood cells from various donors showed considerable intra- and interindividual variability . Incubation of CP-treated blood sample s at 37 degrees C caused a rapid decrease in DNA effects , but DNA migration was still significantly increased 1 hr after the end of the CP treatment . Comparative studies with the in vitro sister chromatid exchange ( SCE ) test were performed that demonstrated that much lower CP concentrations ( about 100 times ) were required for a significant induction of SCEs .  A group of 11 patients who suffered from vasculitis/collagen disease and were treated with low CP doses ( 50 - 200 mg/day ) exhibited an elevated level of DNA damage in the SCG test with peripheral blood cells , compared with a group of 11 control persons or 5 patients without chemotherapy .  Increases in DNA damage were variable and not clearly related to the CP dose . SCE tests could successfully be performed with 5 out of the 11 CP-treated patients ; all showed significantly increased SCE frequencies . For six patients no result could be obtained with the SCE test due to a failure of lymphocyte proliferation .  Three multiple sclerosis patients who received high doses of CP were investigated with the SCG test before , during , and after the treatment . The results indicate that CP-induced DNA effects that are detectable with the SCG test persist in vivo for a period of several days , but for less than 2 weeks . The results of our study provide information with regard to the use of the SCG test in human monitoring . The advantages and limitations of the test are discussed Objectives : This study evaluates by comet assay the induction of early DNA damage in healthcare workers of an oncology hospital regularly h and ling antineoplastic drug mixtures . The aim was to identify a suitable biomarker of DNA damage by exposure to low levels of such drugs . Methods : We studied 12 day hospital nurses and 13 oncology ward nurses who performed up to 300 and up to 35 drug administrations per week , respectively , and five pharmacy employees who regularly prepared mixtures of antineoplastic agents . Thirty healthy subjects were selected as controls . For exposure evaluation , we performed environmental monitoring of 5-fluorouracil , cytarabine , gemcitabine , cyclophosphamide , and ifosfamide in selected work areas of pharmacy and day hospital units and biological monitoring of urine for the 5-fluorouracile metabolite , α-fluoro-β-alanine . We evaluated early DNA damage in lymphocytes and exfoliated buccal cells by comet assay measuring tail moment ( TM ) parameter that indirectly indicates the presence of DNA damage . Results : Environmental monitoring detected cyclophosphamide , 5-fluorouracil and ifosfamide , with higher levels of contamination in day hospital unit . The biological monitoring measured detectable levels of α-fluoro-β-alanine only in three nurses . Comet assay showed an increase on exfoliated buccal cells , even if not statistically significant , of mean TM with respect to controls in day hospital nurses ( 43.2 vs. 28.6 , respectively ) while ward nurses and pharmacy technicians did not show differences . Comet assay performed on lymphocytes did not show appreciable differences between exposed and controls . Conclusions : The employment of the sensitive comet assay , which is able to detect early the effects of a recent exposure to genotoxic substances , allowed us to find a slight DNA damage , only on exfoliated buccal cells of day hospital nurses , the group h and ling the highest amount of drugs during the administration process . This finding suggests that comet assay on exfoliated buccal cells could represent a useful tool to evaluate early and still repairable genotoxic effects of exposure to antineoplastic drug mixtures and then contribute to the improvement of the hospital safety practice 
    Output:
    
Conclusions : A mixture of personal parameters , comet assay method ological variables , and exposure characteristics may be responsible for heterogenic data from comet assay studies and interfere with obtaining conclusive results .