A diagnosis of gastric cancer does not mean that the diagnosis is complete; physicians also need to evaluate the depth of tumor infiltration, the extent of infiltration, and lymph node metastasis, because these are important factors that influence treatment decisions for gastric cancer. So, what means will the doctor take to evaluate the tumor?
CT and ultrasound endoscopy (EUS)
Enhanced CT and EUS are usually the two most important tests to assess the depth of infiltration, extent of infiltration, lymph node metastasis, etc. of gastric cancer. Patients with a definite diagnosis of gastric cancer are usually given an enhanced CT and EUS.
The role of ultrasound endoscopy in gastric cancer diagnosis and treatment
Both enhanced CT and EUS can grade the depth of local infiltration and lymph node metastasis of gastric cancer, assess outcomes, and perform preoperative T-grading (depth of local infiltration) and N-grading (extent of lymph node metastasis) on patients.
However, the accuracy of these two tests is still limited by technical constraints. Compared with postoperative pathological staging, the accuracy of EUS is reported to be 57%-88% for T-staging and 30%-90% for N-staging, and the accuracy of enhanced CT is reported to be 43%-82% for T-staging. The accuracy of these examinations also varies among different treatment centers. The two tests can also complement each other in the assessment of treatment.
In addition, physicians may perform enhanced CT scans of the chest, abdomen, and pelvis to clarify the presence of metastases in these common metastatic sites of gastric cancer.
Magnetic resonance imaging (MRI)
MRI has advantages in imaging soft tissue, and some studies suggest that it can complement enhanced CT.
MRI can clearly show the relationship between the lesion and the surrounding anatomy and determine whether there is direct invasion. Some studies have shown that MRI can clearly demonstrate direct invasion of the pancreas and lymph node enlargement in gastric cancer. However, MRI does not show small cancer foci well. Therefore, the use of MRI should be combined with CT and EUS.
Positron emission computed tomography imaging (PET-CT)
Some studies have shown that PET-CT is more accurate than enhanced CT for preoperative staging of gastric cancer and that PET-CT can perform a single whole-body examination, which helps detect distant metastases early.
PET-CT has the advantage of distinguishing malignant tumors from reactive hyperplastic or fibrotic changes in cases where conventional examination is difficult. In terms of lymph node detection, CT tends to miss metastatic lymph nodes smaller than 10 mm and does not easily distinguish reactive hyperplastic lymph nodes from tumor metastases, whereas PET-CT can distinguish metastatic lymph nodes 5 mm in size and obtain metabolic information, improving the detection rate of lesions.
However, the use of PET-CT has limitations, as it is expensive, not available in many primary care hospitals, and has high radiation exposure. Some studies have shown that the current radiation dose of PET-CT is commonly as high as 70Gy, and this dose has a considerable impact on the long-term toxicity and long-term outcome of patients. Therefore, the physician will decide whether to perform this test based on the patient’s actual condition.
Laparoscopic exploration with cytologic screening
Preoperative laparoscopic exploration with cytologic screening is an important test to assess for peritoneal metastases in patients with suspected peritoneal metastases, thus avoiding the embarrassing situation of intraoperative detection of peritoneal metastases that would prevent continuation of radical resection.
In conclusion, enhanced CT and EUS are important tools for the evaluation of patients with confirmed gastric cancer, in addition to MRI, PET-CT, and laparoscopic exploration with cytologic screening, which are used optionally for a complete evaluation of the tumor. (Contributed by Gao Peng, Department of Gastrointestinal Oncology, The First Hospital of China Medical University)