Purpose (diagnosis/evaluation)	Grade I recommendations	Grade II recommendations	Grade III recommendations
Definitive diagnosis	Gastroscopy + biopsy (Evidence 1A)	Cytological examination (Evidence 2A)a
Location evaluation	• Gastroscopy (Evidence 1A) • Abdominal enhanced CT (Evidence 1A)	Abdominal MRI (Evidence 2A)	X‐ray barium double contrast radiography (Evidence 2B)
Staging evaluation	• Abdominal and pelvic enhanced CTb (Evidence 1B) • Chest CTc (Evidence 1B) • EUSd (Evidence 1A)	• Abdominal MRIe (Evidence 2A) • PET/CT (Evidence 2A) • Diagnostic laparoscopy and examination of intraperitoneal washingsf (Evidence 1B)
Treatment efficacy evaluation	Abdominal and pelvic enhanced CTg (Evidence 1A)	• Gastroscopy (Evidence 2A) • PET/CT (Evidence 1B) • Abdominal MRI (Evidence 2A)	Functional imaging examinationh (Evidence 3)

Abbreviations: EUS, endoscopic ultrasound; MRI, magnetic resonance imaging; PET/CT, positron emission tomography/computed tomography;

Notes

^aIf it is not possible to obtain a pathological diagnosis of gastric cancer despite repeated gastroscopic biopsies, cytological examination of ascites/pleural effusion or pathological examination of metastatic lesions can be used as the basis for qualitative diagnosis.

^bEnsure that the gastric cavity is fully dilated and expanded by drinking enough liquid, water preferably, before the examination [4, 5]. A multiphase and multi‐planar enhanced contrast scan is recommended for diagnosis [6]. Plain abdominal CT scans are not recommended. If patients have contraindications to the contrast agent used for enhanced CT scan, MRI or EUS is recommended [4, 5]. CT imaging texture analysis can be used for assisting physicians’ evaluation and could potentially increase staging accuracy [7].

^cChest CT can detect lung metastasis more effectively than X‐ray examination [6]. For EGJ carcinoma, enhanced CT scan of the chest is recommended to assess the metastatic status and range of mediastinal lymph nodes.

^dEUS should be carried out in qualified centers. In the 8th edition of the AJCC/UICC staging system for gastric cancer, esophageal cancer, and EGJ cancer, EUS is recommended as the preferred modality for the clinical evaluation of tumor depth invasion (cT) [5]. EUS cT staging not only enables direct observation of the lesions but can also provide visual descriptions regarding the different anatomical layers of the gastric wall and non‐homogeneous hypoechoic regions which could suggest the destruction of corresponding layers of the gastric wall. Simultaneously, EUS can detect enlarged perigastric lymph nodes and metastatic lesions in the gastric‐neighboring parts of the liver and peritoneal cavity. Thus, EUS is helpful for the diagnosis and clinical staging of gastric cancer, and assessment of response to neoadjuvant therapy. A systematic meta‐analysis of 50 studies (n = 4397) reported that the overall sensitivity and specificity of EUS for distinguishing T1 to T2 (superficial) versus T3 to T4 (advanced) gastric cancer was 0.86 and 0.90, respectively [8]. Further, the diagnostic capacity of EUS to distinguish T1 (early gastric cancer) versus T2 (muscle‐infiltrating) tumor was 0.85 and 0.90, and T1a (mucosal) versus T1b (submucosal) cancer was 0.87 and 0.75, respectively [8].

^eWhen liver metastasis is suspected on a CT scan, abdominal contrast MRI is recommended for further confirmation. If the patients’ conditions permit, a liver‐specific contrast agent can be used to increase the diagnostic sensitivity [9].

^fDiagnostic laparoscopic exploration and examination of intraperitoneal washings are recommended for detecting occult metastasis and when peritoneal metastasis is suspected [5]. For intraperitoneal lavage, 200 mL of normal saline can be infused into the different quadrants of the abdominal cavity and collect ≥50 mL of the lavage fluid for cytological examinations.

^gAccording to the response evaluation criteria in solid tumors (RECIST) 1.1 criteria [10], nodules of the liver, lung, or peritoneal metastasis with a long‐axis diameter ≥1 cm or lymph nodes with a short‐axis diameter ≥1.5 cm should be used as target lesions for treatment evaluation. The thickness of primary lesions can be used as a reference for therapeutic assessment but should not be considered as a target lesion. In regard to immunotherapy, treatment efficacy can be evaluated using the iRECIST criteria [11].

^hSmall sample‐sized studies have shown that volume measurement on imaging examinations [12] and functional imaging parameters such as the apparent diffusion coefficient value of diffusion‐weighted MRI (DW‐MRI) [13] and iodine concentration of spectral CT examinations [14] can assist in the evaluation of treatment efficacy of gastric cancer and can be used as a reference for evaluating treatment of atypical cases. Further, CT deep learning technology has also shown potential in assisting the evaluation of gastric cancer chemotherapy efficacy [15].