***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: BACKGROUND The majority of patients with primary or metastatic malignancies confined to the liver are not c and i date s for resection because of tumor size , location , multifocality , or inadequate functional hepatic reserve . Cryoablation has become a common treatment in select groups of these patients with unresectable liver tumors . However , hepatic cryoablation is associated with significant morbidity . Radiofrequency ablation ( RFA ) is a technique that destroys liver tumors in situ by localized application of heat to produce coagulative necrosis . In this study , we compared the complication and early local recurrence rates in patients with unresectable malignant liver tumors treated with either cryoablation or RFA . PATIENTS AND METHODS Patients with hepatic malignancies were entered into two consecutive prospect i ve , nonr and omized trials . The liver tumors were treated intraoperatively with cryoablation or RFA ; intraoperative ultrasonography was used to guide placement of cryoprobes or RFA needles . All patients were followed up postoperatively to assess complications , treatment response , and local recurrence of malignant disease . RESULTS Cryoablation was performed on 88 tumors in 54 patients , and RFA was used to treat 138 tumors in 92 patients . Treatment-related complications , including 1 postoperative death , occurred in 22 of the 54 patients treated with cryoablation ( 40.7 % complication rate ) . In contrast , there were no treatment-related deaths and only 3 complications after RFA ( 3.3 % complication rate , P<0.001 ) . With a median follow-up of 15 months in both patient groups , tumor has recurred in 3 of 138 lesions treated with RFA ( 2.2 % ) , versus 12 of 88 tumors treated with cryoablation ( 13.6 % , P<0.01 ) . CONCLUSIONS RFA is a safe , well-tolerated treatment for patients with unresectable hepatic malignancies . This study indicates that ( 1 ) complications occur much less frequently following RFA of liver tumors compared with cryoablation of liver tumors , and ( 2 ) early local tumor recurrence is infrequent following RFA OBJECTIVES To analyze sources search ed in Cochrane review s , to determine the proportion of trials included in review s that are indexed in major data bases , and to compare the quality of these trials with those from other sources . METHODS All new systematic review s in the Cochrane Library , Issue1 2001 , that were restricted to r and omized controlled trials ( RCTs ) or quasi- RCTs were selected . The sources search ed in the review s were recorded , and the trials included were checked to see whether they were indexed in four major data bases . Trials not indexed were checked to determine how they could be identified . The quality of trials found in major data bases was compared with those found from other sources . RESULTS The range in the number of data bases search ed per review ranged between one and twenty-seven . The proportion of the trials in the four data bases were Cochrane Controlled Trials Register = 78.5 % , MEDLINE = 68.8 % , Embase = 65.0 % , and Science/Social Sciences Citation Index = 60.7 % . Search ing another twenty-six data bases after Cochrane Controlled Trials Register ( CCTR ) , MEDLINE , and Embase only found 2.4 % additional trials . There was no significant difference between trials found in the CCTR , MEDLINE , and Embase compared with other trials , with respect to adequate allocation concealment or sample size . CONCLUSIONS There was a large variation between review s in the exhaustiveness of the literature search es . CCTR was the single best source of RCTs . Additional data base search ing retrieved only a small percentage of extra trials . Contacting authors and manufacturers to find unpublished trials appeared to be a more effective method of obtaining the additional better quality trials HYPOTHESIS The complication and success rates in patients treated with either percutaneous cryosurgery ( PCS ) or percutaneous radiofrequency ( PRF ) for unresectable hepatic malignancies are similar . DESIGN Retrospective study . SETTING University hospital . PATIENTS AND METHODS Sixty-four patients were treated with either PCS  ( n = 31 ) or PRF ( n = 33 ) . Patient treatment was based on the r and om availability of the probes . Tumors were evaluated by a blinded comparison of pretreatment and posttreatment helical computed tomographic scans . All living patients had at least a 6-month follow-up . MAIN OUTCOME MEASURES Complication rate , initial treatment success ( complete devascularization of the tumor ) , and local recurrence ( tumor revascularization within or at its periphery ) . RESULTS The distribution of tumor types was similar in the 2 groups ( P = .76 ) . One patient with cirrhosis died of variceal hemorrhage on day 30 after PCS ( mortality , 3.2 % ) , while no mortality was observed after PRF ( P = .48 ) . Complications occurred in 9 ( 29 % ) of the patients following PCS and in 8 ( 24 % ) of the patients following PRF ( P = .66 ) . Initial treatment success was comparable in the 2 treatment groups ( 30 [ 83 % ] of 36 tumors following PCS vs 34 [ 83 % ] of 41 tumors following PRF ) . However , local recurrences occurred more frequently after PCS than after PRF ( 16 [ 53 % ] of 30 vs 6 [ 18 % ] of 34 ; P = .003 ) . The higher rate of local recurrence was identified for metastases ( 10 [ 71 % ] of 14 after PCS vs 3 [ 19 % ] of 16 after PRF ; P = .004 ) , while the difference was not significant for hepatocellular carcinoma ( 6 [ 38 % ] of 16 after PCS vs 3 [ 17 % ] of 18 after PRF ; P = .25 ) . Multivariate analysis demonstrated that the use of PCS ( P = .003 ) and more than 1 treatment ( P = .05 ) were independent risk factors for local tumor recurrence . CONCLUSION While similar initial treatment success and complication rates are observed following either PCS or PRF , local recurrences occur more frequently following PCS , particularly for metastases BACKGROUND Thermal ablation of unresectable hepatic tumors can be achieved by cryosurgical ablation ( CSA ) or radiofrequency ablation ( RFA ) . The relative advantages and disadvantages of each technique have not yet been determined . HYPOTHESIS Radiofrequency ablation of malignant hepatic neoplasms can be performed safely , but is currently limited by size . Cryosurgical ablation , while associated with higher morbidity , is more effective for larger unresectable hepatic malignant neoplasms . DESIGN Retrospective analysis of prospect i ve patient data base . PATIENTS AND METHODS Between July 1992 and September 1999 , 308 patients with liver tumors not amenable to curative surgical resection were treated with CSA and /or RFA ( percutaneous , laparoscopic , celiotomy ) . No patient had preoperative evidence of extrahepatic disease . All patients underwent laparoscopy with intraoperative ultrasound if technically possible . Both RFA and CSA were performed under ultrasound guidance . Resection , as an adjunctive procedure , was combined with ablation in certain patients . RESULTS Laparoscopy identified extrahepatic disease in 12 % of patients , and intraoperative hepatic ultrasound identified additional lesions in 33 % of patients , despite extensive preoperative imaging . Radiofrequency ablation alone or combined with resection or CSA result ed in reduced blood loss ( P<.05 ) , thrombocytopenia ( P<.05 ) , and shorter hospital stay compared with CSA alone ( P<.05 ) . Median ablation times for lesions greater than 3 cm were 60 minutes with RFA and 15 minutes with CSA ( P<.001 ) . Local recurrence rates for lesions greater than 3 cm were also greater with RFA ( 38 % vs 17 % ) . CONCLUSIONS Laparoscopy and intraoperative ultrasound are essential in staging patients with hepatic malignant neoplasms . Radiofrequency ablation when combined with CSA reduces the morbidity of multiple freezes . Although RFA is safer than CSA and can be performed via different approaches ( percutaneously , laparoscopically , or at celiotomy ) , it is limited by tumor size ( <3 cm ) . Percutaneous RFA should be considered in high-risk patients or those with small local recurrences BACKGROUND / AIMS This study aim ed to assess the main features of hepatocellular carcinoma at the time of diagnosis in Italy , particularly in relation to the presence or absence of underlying cirrhosis , hepatitis virus marker patterns , age of the subjects and alpha-foetoprotein values . METHODS A total of 1148 patients with hepatocellular carcinoma seen at 14 Italian hospitals in the 1-year period from May 1996 to May 1997 were the subjects of this prevalence study . Both newly diagnosed cases ( incident cases ) and cases diagnosed before May 1996 but still attending the hospitals during the study period ( prevalent cases ) were included . RESULTS We found that 71.1 % of cases were positive for hepatitis C virus antibodies but negative for HBsAg ; in contrast , 11.5 % were negative for anti-HCV but positive for HBsAg ; 5.3 % were positive for both markers ; and 12.1 % were negative for both viruses . The mean age of detection was over 60 years , with a younger mean age in HBsAg-positive compared to anti-HCV-positive patients ( 59.3 years vs. 65.6 years , p<0.01 ) . The male-to-female ratio among HBsAg-positive patients was 10.4:1 , in contrast to 2.8:1 among anti-HCV-positive patients ( p<0.01 ) . The majority of cases ( 93.1 % ) had underlying cirrhosis . Cirrhotic patients were more likely to be anti-HCV positive than non-cirrhotic cases ( 73.2 % vs 43.9 % ; p<0.01 ) ; conversely , absence of hepatitis virus markers was more frequently observed in the non-cirrhotic than in the cirrhotic population ( 40.9 % vs. 10.0 % ; p<0.01 ) . Overall , the alpha-foetoprotein level was altered ( > 20 ng/ml ) in 57.9 % of patients ; only 18 % of cases presented diagnostic ( > 400 ng/ml ) values . Anti-HCV positivity ( O.R. 2.0 ; CI 95%=1.3 - 3.1 ) but not HBsAg positivity ( O.R. 1.0 ; CI 95%=0.6 - 1.8 ) was shown to be an independent predictor of the likelihood of altered alpha-foetoprotein values by multivariate analysis . CONCLUSIONS These findings point to differences in the characteristics of the population s infected by hepatitis B and hepatitis C. Factors other than the hepatitis viruses are important in non-cirrhotic patients . A change in the relative prevalence of hepatitis virus markers among hepatocellular carcinoma cases was demonstrated , reflecting a significant change in the rate of HBV endemicity in the Italian population . Finally , the increased trend in the mortality rate from liver cancer in Italy from 4.8 per 100,000 in 1969 to 10.9 in 1994 may reflect the large cohort of subjects infected with HCV via the iatrogenic route during 1950s and 1960s when glass syringes were commonly used for medical treatment Methods for combining data from several studies exist and appear to be quite useful . None satisfactorily addresses the question of what studies should be combined . This issue is the most serious method ological limitation . Even studies with statistically significant interaction might still be combined if the effect were in the same direction . Thus , substantial scientific input is required as to what criteria must be met by each potential study . Much can be learned from combining or pooling data but it must be done cautiously . Pooling exercises do not replace well design ed prospect i ve clinical trials . Efforts for establishing basic design criteria to allow for multicentre and multicountry trials to be more easily combined might be useful . OBJECTIVE The authors evaluate the results of cryosurgery in malignant liver tumors . SUMMARY BACKGROUND DATA The outcome of primary or secondary liver tumors is poor when resection can not be achieved . Encouraging results of cryosurgery have been reported in unresectable liver tumors , but this treatment needs further evaluation of its efficacy in homogeneous groups of patients . METHODS From 63 patients with malignant liver tumors with various histology treated by cryosurgery in a 2.5-year period , the authors evaluated the results of 34 patients with nonresectable hepatocellular carcinoma ( 9 patients ) or nonresectable metastases from colorectal cancer ( 25 patients ) .  Cryosurgery was used either as a single treatment ( 4 hepatocellular carcinomas , 5 metastases ) or in association with liver resection ( 5 hepatocellular carcinomas , 20 metastases ) . Systemic chemotherapy was used routinely before surgery and after surgery . RESULTS There was no intraoperative mortality . Mortality within 2 months was 3 % and was unrelated to the procedure . Postoperative morbidity consisted of one sterile fluid collection and one bili 
    Output:
    
This retrospective study compared percutaneous cryotherapy with percutaneous radiofrequency .
Both severe and non-severe adverse events were reported , but the true nature and extent of harm was difficult to asses .
At present , there is no evidence to recommend or refute cryotherapy for patients with hepatocellular carcinoma .