Staging Methods

Staging methods vary with local facilities and expertise, but a computed tomographic (CT) scan of the chest and abdomen is essential. CT is moderately effective at estimating T-stage, and the

FIGURE 1 Topographical distribution of lymph node stations as defined by the second English edition of the Japanese classification of gastric carcinoma. The numbers indicate the recognized nodal "stations."

involvement of local and regional lymph nodes. It is extremely useful in the detection of lung and liver metastases, where its sensitivity approaches 90% and its specificity 98% (23-25). Endoscopic ultrasound (EUS) is established as a key investigation in esophageal cancer, but is more controversial in gastric cancer. Studies using operative specimen pathology as the "gold standard" indicate that it has an overall accuracy of 80% to 90% for T-stage and 68% to 86% for N-stage (26-30) (evidence level 1). EUS can be particularly useful in demonstrating whether there is direct invasion of the pancreas posteriorly, as this question can be very difficult to determine either by laparoscopy or CT scan, and is very important operatively.

Positron emission tomography (PET) scanning using 5-fluorodeoxy glucose as a probe has proved extremely sensitive in a wide variety of cancers both pre- and post-treatment. Difficulties in defining its exact role have arisen because of its limited availability in many countries, the plethora of other staging tests which predated it, and its relative lack of specificity. As we already have sensitive and specific tests for liver and lung metastases and loco-regional disease, PET (or increasingly PET/CT) currently tends to be used as the arbiter in cases where there is discomfort with the results of other methods. This perhaps reduces its success rate, as these are by definition the most difficult cases. Current evidence suggests that PET/CT has a sensitivity of 98% to 100% and a specificity of up to 89% in detecting lung and liver metastases in gastrointestinal tumors (31-33), but is less effective in detecting peritoneal disease. It appears less effective in gastric than esophageal tumors as the uptake of isotope is usually less avid. There is a considerable need for further research on the appropriate management of patients with very small volume of metastatic disease detected by PET.

Laparoscopy predates the other commonly used staging methods but remains extremely valuable because of its high degree of accuracy for small volume peritoneal disease (34-40). Its sensitivity for peritoneal metastasis is quoted at 96% (41) and its specificity nearly 100%, which compares favorably with the best figures quoted for PET, CT, and other modalities. There is an extensive literature on the use of peritoneal washings for cytology. Using a fairly straightforward lavage and conventional cytological staining, the yield of this technique is fairly low, but the prognostic implications if cancer cells are found are grave (42-45). A recent study has suggested that this may not be so if the tumor is fully staged in other respects, particularly T-stage (46). Most surgeons currently use washings for cytology on a limited basis or not at all. The other benefits of laparoscopy include the ability to pick up small surface liver metastasis missed by CT scanning, and the opportunity for surgeon and anesthetist to assess the response of the patient to a brief anesthetic.

Staging should always include an assessment of fitness for operation, particularly where the surgery may be a significant risk to the patient. The American Society of Anaesthesiologists (ASA) grade and the physiological and operative severity score for enumeration of morbidity and mortality (POSSUM) score component are independent predictors of mortality in large prospective series (47,48), and the Goldman Cardiac Index has been validated in general and vascular surgery, although it seems less predictive than ASA (49-52). An index scoring the preoperative function of multiple organs has been derived by Bartels et al. (53), and has been carefully validated in esophageal cancer patients including many with cancer at the gastro-esophageal junction. Whether this is accurate for gastrectomy patients is unclear. At present, most

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