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Median values for M-stage accuracy of EUS and CT are difficult to estimate, since studies vary widely according to population studied (Table 2). Both EUS and CT have a high percentage of false negatives and corresponding low sensitivity; EUS because of its inability to evaluate most distant sites, and CT because of its insensitivity to small metastatic lesions. When GI tumors first present, they tend to have a low prevalence of metastases, especially if one excludes metastasis to distant lymph nodes. Prevalence of metastases is even lower in a population screened or evaluated for symptoms early. Depending on the type of tumor, 10 to 25% of patients have metastatic disease at the time of presentation, but only one-half to two-thirds of these metastases are detected by radiological imaging. Nevertheless, this low sensitivity decreases accuracy of CT or EUS by only about 10 to 15%, because prevalence of metastatic disease is low and specificity of EUS or CT is high. Thus, the relatively high accuracy values in Table 2 for M stage do not reflect the poor sensitivity of EUS or CT. In general, the sensitivity of EUS or CT in patients with positive metastatic disease is half the value of overall accuracy. Because EUS has good resolution of distant lymph node sites, but about only one third of the liver, and CT images other distant sites and the entire liver, CT and EUS are complementary for M-stage evaluation. Another limitation of EUS is that the echo pattern and features of EUS images of various diseases can appear quite similar. Consequently, differentiating criteria overlap. Some of this overlap is inherent to the ultrasound pulses; however, some of the overlap is a result of limited experience with the interpretation of EUS images. EUS will have a major role in defining abnormal areas less than 10 mm, or those mixed with fibrosis, for directed deep biopsies. Biopsy from the GI lumen through the GI tract wall can histologically establish a diagnosis less invasively than the standard surgical approach. The role of EUS in eliminating the need for surgery in certain patients clearly depends on the definition of those stages that do benefit from surgery. A lesion that has just started to invade a regional vessel or organ (advanced T stage) or a lesion with only 1 or 2 lymph nodes around and adjacent to the tumor, is certainly removable but not "truly resectable." Most esophageal tumors below the upper esophageal sphincter can be removed surgically, with the exception of those involving spread to distant organs, celiac nodes, or deep invasion of the bronchi or the aorta. Removal of a tumor that extends to the margin or into regional nodes is clearly a worse prognostic category than a "truly resectable" lesion still confined to the esophageal wall. Surgery should be attempted for tumors expected to be completely resectable. Palliative debulking of esophageal carcinoma has been shown to decrease quality of life without improving survival. Palliative surgery also delays alternative treatment [25]. However, for gastric or pancreatic carcinomas, a few positive regional lymph nodes do not appear to have as much influence on prognosis. Therefore, malignant regional lymph nodes may not be as important for surgical removal of all visible disease. T stage is probably much more important in this regard. The role of EUS in selecting appropriate patients for surgery will thus depend on alternative treatments available for amelioration of symptoms and improvement of quality of life, survival, and outcome. EUS may eventually define early tumors that are best treated initially by surgical resection, as well as those tumors that have been downstaged with alternative treatments to a resectable lesion. Table 2
a Values are median estimates in percent from references in text. |