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Staging of Stomach Cancer: Current Approaches and Techniques
Introduction to Stomach Cancer Staging
Stomach cancer, also known as gastric cancer, remains a significant global health issue despite declining incidence in some regions. Accurate staging of stomach cancer is crucial for determining the appropriate treatment strategy and predicting patient outcomes. The staging process typically involves assessing the tumor's size and extent (T), lymph node involvement (N), and the presence of distant metastasis (M), collectively known as the TNM staging system.
AJCC 7th Edition Staging System
The 7th edition of the American Joint Committee on Cancer (AJCC) staging manual introduced several changes aimed at improving the accuracy and applicability of gastric cancer staging. One of the key updates was the redefinition of nodal status cutoff values, which led to a more balanced distribution of N1, N2, and N3 groups. This change improved the predictive accuracy of nodal staging, although the overall stage-specific predictive accuracy did not significantly improve compared to the 6th edition .
Imaging Techniques in Stomach Cancer Staging
Computed Tomography (CT)
CT scans are widely used for the preoperative staging of gastric cancer. Advanced CT techniques, such as those using thin sections and optimal contrast enhancement, have improved the accuracy of staging. However, CT has limitations in detecting non-enlarged lymph node metastasis, peritoneal dissemination, and small hematogenous metastasis. The accuracy of CT for clinical N staging is around 63.2%, with higher specificity but lower sensitivity in detecting nodal metastases.
Positron Emission Tomography (PET)
PET scans, particularly those using 2-[fluorine-18]fluoro-2-deoxy-d-glucose (FDG), are valuable for detecting distant metastases in organs such as the liver, lungs, and bones. However, PET is not suitable as a first-line diagnostic tool for tumor staging but can be useful in monitoring the response to chemotherapy.
Endoscopic Ultrasonography (EUS)
EUS is considered the gold standard for local (T) staging of gastric cancer. It provides high accuracy in assessing the depth of tumor invasion and regional lymph node status. Studies have shown that EUS has a diagnostic accuracy ranging from 65% to 92.1% for T staging and is particularly effective in assessing serosal involvement . EUS is also useful in predicting the resectability of tumors, with high accuracy in identifying stages T1 to T3, which correspond to R0 resectability (no residual tumor).
Magnetic Resonance Imaging (MRI)
MRI is another imaging modality used in the local staging of gastric cancer. It offers similar diagnostic accuracy to EUS and CT, particularly in assessing serosal involvement. However, fewer studies have been conducted on MRI, making EUS the preferred choice for preoperative T staging.
Diagnostic Laparoscopy
Diagnostic laparoscopy is a valuable technique for staging stomach cancer, particularly in detecting intra-abdominal metastasis that may be missed by CT. It has shown higher accuracy in T and N staging compared to CT, making it an important tool in the preoperative assessment of gastric cancer.
Conclusion
Accurate staging of stomach cancer is essential for effective treatment planning and prognosis. The AJCC 7th edition staging system has made significant strides in improving nodal staging accuracy. Imaging techniques such as CT, PET, EUS, and MRI each have their strengths and limitations, with EUS being the most reliable for local staging. Diagnostic laparoscopy also plays a crucial role in detecting metastasis and refining the staging process. Future advancements and refinements in these techniques will continue to enhance the accuracy and effectiveness of gastric cancer staging.
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