Stomach cancer study may spare some patients unnecessary surgery

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: 1. Upfront surgery cohort * Patients who underwent radical surgery for gastric cancer at Zhongshan Hospital, Fudan University. * Patients who did not receive neoadjuvant chemotherapy, radiotherapy, immunotherapy, or other antitumor treatments that may affect the pathological assessment of the primary tumor or lymph node metastasis before surgery. * Patients with pathologically confirmed gastric adenocarcinoma or gastroesophageal junction adenocarcinoma after surgery, including Siewert type II and III tumors only. * Patients with definite pathological assessment of lymphatic invasion and regional lymph node status. * Patients with available and definite MMR status. 2. ESD cohort * Patients who underwent ESD for gastric cancer at Zhongshan Hospital, Fudan University. * Patients with pathologically confirmed gastric adenocarcinoma or gastroesophageal junction adenocarcinoma after ESD, including Siewert type II and III tumors only. * Patients with complete post-ESD pathological information, including histological type, depth of invasion, tumor size, ulcerative findings, lymphatic invasion status, venous invasion status, horizontal margin status, and vertical margin status. * Patients with available and definite MMR status. Exclusion Criteria: 1. Upfront surgery cohort * Patients with other pathological types, such as gastric squamous cell carcinoma or neuroendocrine carcinoma. * Patients who received neoadjuvant treatment before surgery, including chemotherapy, radiotherapy, immunotherapy, targeted therapy, or other systemic antitumor treatments. * Patients with missing postoperative pathological information, resulting in inability to determine lymphatic invasion or regional lymph node metastasis status. * Patients with missing or indeterminate MMR status. * Patients with concurrent malignancies that may interfere with the determination of the origin of lymph node metastasis. 2. ESD cohort * Patients with other pathological types, such as gastric squamous cell carcinoma or neuroendocrine carcinoma. * Patients with missing post-ESD pathological information that precludes eCURA classification, eCURA risk score calculation, or assessment of lymphatic invasion status. * Patients with missing or indeterminate MMR status.