***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 There is a need to assess the sensitivity , specificity , and predictive value of endoscopic ultrasonography ( EUS ) in the diagnosis and staging of gastric cancer and lymphoma . METHODS A prospect i ve study was performed on 86 patients with endoscopic gross appearance suspicious for cancer or lymphoma .  Biopsies with endoscopic forceps were always carried out before EUS . All patients underwent laparotomy for final diagnosis , staging , and eventually treatment . The results of EUS were correlated with the histologic findings of the resected specimens , when possible , or with the surgical findings . There were 42 gastric cancers and 44 primary gastric lymphomas . RESULTS EUS made a correct diagnosis of cancer in 35 of 42 patients , with a sensitivity of 83 % . Positive predictability was 87 % , specificity was 97 % , and negative predictability was 96 % . Diagnostic accuracy was 95 % . In the evaluation of cancer depth invasion , EUS was correct in 91 % of cases . EUS displayed perigastric metastatic lymph nodes in 14 of 25 patients , with a sensitivity of 56 % . Positive predictive value was 93 % , specificity was 93 % , and negative predictive value was 54 % . Diagnostic accuracy was 69 % . EUS made a correct diagnosis of lymphoma in 39 of 44 patients , with a sensitivity of 89 % . Positive predictability was 87 % , specificity was 97 % , and negative predictability was 97 % . Diagnostic accuracy was 95 % . In the evaluation of lymphoma depth invasion , EUS was correct in 92 % of cases . EUS displayed metastatic perigastric lymph nodes in 8 of 18 patients , with a sensitivity of 44 % . Positive predictability was 100 % , specificity was 100 % , and negative predictability was 72 % . Diagnostic accuracy was 77 % . CONCLUSIONS From these data it appears that in these diseases EUS has demonstrated specific ultrasonographic features that allow correct diagnosis and staging in the majority of patients . In difficult cases EUS may help to achieve the correct diagnosis . EUS also appear to be a useful tool for staging of gastric cancer and lymphoma . It shows not only tumor depth and local spread but also the passage from a pathologic to a normal wall and lymph node metastasis . With this accurate noninvasive staging procedure , in the near future many patients will no longer undergo exploratory laparotomy for surgical staging . Thanks to EUS , the choice of conservative or surgical treatment can be strongly affected . In case of surgery , EUS can orient the kind of surgical approach . Moreover , the use of EUS for evaluation of therapy during follow-up will probably become of major importance Prospect ively , 72 patients with a gastric carcinoma were  studied endosonographically before surgery . The results were correlated with those obtained with the histology of resected specimens according to the new ( 1987 ) TNM classification . Endoscopic ultrasonography ( EUS ) was accurate in assessing the extent and depth of tumor infiltration .  Early gastric carcinoma could readily be distinguished from advanced carcinoma . The overall accuracy of EUS was 84.7 % . Occasionally , overstaging and understaging occurred . Stenosis was a factor limiting accurate staging . EUS was reasonably accurate in the assessment of lymph node metastasis . The overall accuracy was 81.0 % . In non-metastatic lymph nodes , however , the accuracy was only 50 % . Difficulties occurred in distinguishing granulomatous lymph nodes and small micrometastatic lymph node involvement . EUS was not accurate in diagnosing distant metastasis , due to the limited depth of penetration of ultrasound . Technical improvements such as a reduction in the diameter of the echoprobe , and the use of the biopsy channel for EUS-guided cytological puncture will further enhance the accuracy of EUS Strategies for the treatment of cancer of the oesophagus depend on the tumour stage at the time of diagnosis . Resection , the only curative treatment , is confined to early tumour stages . Tumours with local infiltration are usually unresectable and require palliative treatment . Computed tomography has been widely used for preoperative staging but often fails to define this correctly . Endoscopic ultrasound allows direct visualisation of the parietal wall and may be useful in staging gastrointestinal tumours . In a comparative prospect i ve study , 52 patients with tumours of the oesophagus were investigated preoperatively both by endoscopic ultrasound and computed tomography to determine the stage of tumour infiltration and local lymph node involvement . Thirty seven of these patients underwent operation , resection , or dissection and entered the study . The intraoperative findings or the histopathological assessment , or both , were taken as a reference . For all TN stages of oesophageal tumours , correct preoperative staging was accomplished by endoscopic ultrasound in 89 % for T stage and 69 % for N stage compared with 51 % and 51 % respectively by computed tomography ( highly significant using Fisher 's exact test ) . This study shows that endoscopic ultrasound is useful in preoperative TN staging of tumours of the oesophagus The dem and for evidence -based healthcare is increasing nationally and internationally and it is equally necessary in both diagnostic and therapeutic practice . Evidence may be collected and combined by means of a systematic literature review of published and unpublished data on a well-defined topic . The output of such review s is then available to guide health policy , influence good practice or direct research . Published guidelines are available on the performance of systematic review s , especially those of r and omized controlled trials . Although there is an extensive literature base of research data in diagnostic imaging there are few such trials , but it is still possible to perform systematic review s. With the alternative study design s encountered it is important to be aware of the main threats to study validity . In this paper the biases likely to be encountered in studies of diagnostic performance are review ed , with particular reference to diagnostic imaging tests . The biases are sub-divided into three categories . The first category is patient selection and covers the validity of generalizing results beyond the study population . The other two , concerning study design and execution and the interpretation of results , affect the likely validity of the results of a study . An underst and ing of these factors is an essential prerequisite for those undertaking or using a systematic literature review in the field of diagnostic imaging . The definitions form the foundations of a defensible review protocol From 1986 to 1990 a prospect i ve comparative study was undertaken to compare the relative accuracy of computed tomography , endogastric ultrasonography , and intraoperative surgical assessment in evaluating the depth of invasion ( T category ) and involvement of lymph nodes ( N category ) of patients with gastric carcinoma . One hundred and eight consecutive patients , who were treated by total gastrectomy and previously evaluated with computed tomography , endogastric ultrasonography , and intraoperative surgical assessment , entered the study . Results ( T and N category ) were compared with those of histopathological staging ( pT and pN category ) . T categories were correctly staged in 43 % of cases with computed tomography , 86 % with endogastric ultrasonography , and 56 % with intraoperative surgical assessment . Computed tomography scanning correctly staged 51 % of all N1 and N2 lymph nodes compared with 74 % for endogastric ultrasonography and 54 % for intraoperative surgical assessment . In general , computed tomography was more accurate for advanced stages of cancer and showed a tendency to overstage the T category and understage N category of gastric tumours . By contrast , endogastric ultrasonography was equally accurate for all T categories and showed an understaging for N categories . Intraoperative surgical assessment overstaged early T stages , understaged T4 tumours , and was equally accurate for all grade s of N categories . Computed tomography scanning and intraoperative surgical assessment of T and N categories were of little value in staging of gastric carcinoma . Endogastric ultrasonography is more accurate than computed tomography scanning and intraoperative surgical assessment . Therefore endogastric ultrasonography should be introduced in the preoperative assessment of patients with gastric carcinoma BACKGROUND Uncontrolled studies suggest that a combination of chemotherapy and radiotherapy improves the survival of patients with esophageal adenocarcinoma . We conducted a prospect i ve , r and omized trial comparing surgery alone with combined chemotherapy , radiotherapy , and surgery . METHODS Patients assigned to multimodal therapy received two courses of chemotherapy in weeks 1 and 6 ( fluorouracil , 15 mg per kilogram of body weight daily for five days , and cisplatin , 75 mg per square meter of body-surface area on day 7 ) and a course of radiotherapy ( 40 Gy , administered in 15 fractions over a three-week period , beginning concurrently with the first course of chemotherapy ) , followed by surgery . The patients assigned to surgery had no preoperative therapy . RESULTS Of the 58 patients assigned to multimodal therapy and the 55 assigned to surgery  , 10 and 1 , respectively , were withdrawn for protocol violations . At the time of surgery , 23 of 55 patients ( 42 percent ) treated with preoperative multimodal therapy who could be evaluated had positive nodes or metastases , as compared with 45 of the 55 patients ( 82 percent ) who underwent surgery alone ( P<0.001 ) . Thirteen of the 52 patients ( 25 percent ) who underwent surgery after multimodal therapy had complete responses as determined pathologically . The median survival of patients assigned to multimodal therapy was 16 months , as compared with 11 months for those assigned to surgery alone ( P=0.01 ) . At one , two , and three years , 52 , 37 , and 32 percent , respectively , of patients assigned to multimodal therapy were alive , as compared with 44 , 26 , and 6 percent of those assigned to surgery , with the survival advantage favoring multimodal therapy reaching significance at three years ( P=0.01 ) . CONCLUSIONS Multimodal treatment is superior to surgery alone for patients with resectable adenocarcinoma of the esophagus The T stage is an important criterion for determining prognosis in esophageal carcinoma .  Endosonography , although established as a highly accurate method in preoperative determination of the T stage , may be less reliable in non-traversable tumor stenoses . In a comparative prospect i ve study , 41 patients with carcinoma of the esophagus were investigated to determine the role of tumor stenosis on the accuracy of endosonography in preoperative T staging . The results were correlated with the histology of the resected specimen . The overall accuracy in T staging with endosonography was 76 % , compared with 49 % in computed tomography .  T staging results of endosonography were good in easily and non-traversable stenoses ( 92 % , 87 % respectively ) , but lower accuracy was obtained in stenoses which could be traversed only with difficulty ( 46 % ) . Computed tomography was inferior to endosonography in all three groups of patients . The high accuracy of  endosonography  in non-traversable stenoses might be due to the fact that all tumors were in an advanced stage ( T3 or T4 ) . When passage of the echoendoscope proves difficult , the low focal distance between the ultrasonic transducer and tumor may hamper clear visualisation of the wall layers and tumor penetration depth . These limitations of endosonography should stimulate further efforts in improving ultrasonic resolution in these cases BACKGROUND AND STUDY AIMS Endosonographic staging of esophageal carcinoma may be limited by non-traversable tumor stenoses . Dilation of malignant esophageal strictures carries a significant risk of esophageal perforation . We therefore evaluated the use of ultrasonic miniprobes in the staging of stenotic esophageal carcinoma compared with conventional endoscopic ultrasound . PATIENTS AND METHODS In a blinded , prospect i ve study , which included histopathological evaluation , 53 consecutive patients ( 43 male , 10 female , mean age 61 years ) with stenosing esophageal carcinomas were examined preoperatively . Endosonography was done using the optical GF-UM3 echo endoscope . If tumor strictures were not traversable with this instrument , a blind esophagoprobe , the MH-908 was used for endosonography . Miniprobe sonography ( MPS ) was done during esophagoscopy in all patients . The various imaging modalities were assessed in terms of complete tumor traversability and correct tumor staging . Every patient underwent surgical tumor resection . RESULTS MPS of the esophagus and proximal parts of the stomach was possible in all 53 patients without prior dilation of tumor stenoses . Endosonography with the GF-UM3 instrument was precluded in 23 patients ( 43.4 % ) while in 20 of the latter patients the MH 908 esophagoprobe could be passed through tumor stenoses . The overall accuracy rates for depth of tumor infiltration ( T ) staging were : 62 % ( 31/50 ) for endosonography ( GF-UM3 plus esophagoprobe ) and 86.8 % ( 46/53 ) for MPS . The accuracy rates for T staging in tumors traversable both with the GF-UM3 echo endoscope and with miniprobes were 56.7 % ( 17/30 ) for GF-UM3 and 8 
    Output:
    
In articles that compared EUS directly with incremental computed tomography , EUS performed better .
EUS is highly effective for discrimination of stages T1 and T2 from stages T3 and T4 for primary gastro-oesophageal carcinomas .
The failure rate of EUS from non-traversability of a stenotic cancer may be a limitation in some patient groups