During the past 10 years, echoendoscopy, or endoscopic ultrasonography (EUS), has proven to be the most significant advance for imaging the gastrointestinal (GI) tract wall and contiguous organs. The detailed resolution seen on EUS images is unmatched by any other current method. Many studies document the high accuracy

of nonoperative GI tumor characterization and staging that is possible with EUS [1]. EUS can provide unique information essential to diagnosing malignancy that is often otherwise obtainable only by surgical techniques. In terms of patient outcome, the role of EUS is clearly woven into the influence of pathological staging strategies and effective treatment on both prognosis and quality of life.

The American joint Committee on Cancer (AJCC) and The International Union Against Cancer (UICC) have each published a manual with recommendations for stage groupings of cancer at all anatomical sites [2,3]. These evolving recommendations are based on contributions from 400 expert participants over 25 years. The AJCC and the UICC, after numerous meetings, reached uniform recommendations to allow the development of I system of staging that would replace other nonuniform methods. This system for staging cancer is now accepted and used worldwide with the hope that "accurate staging of cancer will be most helpful in arriving at decisions regarding appropriate treatment of malignant tumors and in determining prognosis and end results [2]."

For most cancer sites, the staging recommendations were concerned only with anatomical extent of disease. Because an untreated primary cancer or tumor (T) progressively increases in size, regional lymph node (N) involvement occurs, and finally, as a result of continued extension of disease, distant metastasis (M) occurs to distant lymph nodes or organs. TNM classification and stage grouping is thus a method of designating the extent of a particular type of cancer as it is related to its natural course. For certain types of tumors, other factors, including grade, extent of differentiation, and age of the patient, were considered in staging. In the future, biological markers and other parameters may also be factors. For sarcomas, histological analysis and tumor grade may prove to be most important. In certain types of tumors, such as lymphomas, a different system for classification and staging is necessary to effectively define prognosis and to allow changes in therapy to improve outcome and quality of life.

The TNM tumor staging method has proven to be very accurate in determining prognosis; however, for GI tumors, the impact of this system on patient treatment and outcome has been held back by the limited accuracy of techniques for nonoperative staging, as well as by the limited success of various therapeutic options. Until 1 decade ago, results of chemotherapy or radiotherapy for GI tumors were disappointing because these solid tumors have low growth fractions, as well as cells in both cycling and noncycling phases. Decreased sensitivity to antineoplastic agents, which selectively kill the actively dividing cells, resulted from the marked decline in the growth fraction of GI tumors by the time they were detected [4]. Surgery for resection, palliation, or diagnosis and staging was usually attempted in all but the most advanced cases. However, as more sophisticated and effective treatments involving chemotherapy/radiotherapy combined with surgery have evolved, increased response rates and improved survival have been reported [5- 10]. Studies show that accurate staging is essential in determining the timing and dosage of these treatments for greatest efficacy. Accurate preoperative staging can now have a greater impact on patient outcome. Therapeutic procedures, even if not curative, may alter the course and life history of GI cancer.

After discussing EUS methodology, the role of EUS in planning combined chemotherapy, radiotherapy, and surgical treatment is reviewed. In addition, the uses of EUS in benign disease are addressed as they relate to establishing a diagnosis.