OBJECTIVETo investigate the accuracy of CT in preoperative discrimination of cT3 from cT4 in patients with Siewert II esophagogastric junction (EGJ) adenocarcinoma according to UICC/AJCC 8th edition and IGCA 4th edition.

METHODSCT imaging data of 43 consecutive patients with Siewert II EGJ adenocarcinoma who underwent preoperative CT and were diagnosed as pT3 or pT4 by postoperative pathology were retrospectively analyzed. Inclusion criteria were as follows:(1)no previous history of gastric operation, radiochemotherapy, targeted treatment; no contraindications of CT enhanced scanning; (2) good filling of gastric cavity by CT, clear image without artifacts, all axial-coronal-sagittal 3-plane reconstruction images obtained by abdominal stage 3 enhanced scan; (3) operation within 1 week after CT examination; (4) Siewert II EGJ adenocarcinoma confirmed by operation, pT3 and pT4 by postoperative pathology. Transverse and multiplanar reconstruction images were reviewed by two radiologists in double-blind method. Distance between cancer epicenter and esophagogastric junction line, and the contour of the serosa were retrospectively measured on CT scans. The cT staging judgment was performed according to the UICC/AJCC 8th edition (Siewert II EGJ adenocarcinoma should be staged as esophageal cancer) and IGCA 4th edition (Siewert II EGJ adenocarcinoma should be staged as gastric cancer) respectively. Consistency of cT staging and pathological pT staging was compared between UICC/AJCC and IGCA.

RESULTSPreoperative CT revealed that the mean length between tumor epicenter and esophagogastric junction line was(1.5±0.4) cm (0.7-2.5 cm), and such length was ≤2 cm in 41 cases, whose concordance with surgical judgment was 95.3%(41/43). IGCA staging: 18 cases were preoperatively assessed as cT3 and 25 cases as cT4a. UICC/AJCC staging: 41 cases with cancer epicenter locating within 2 cm below esophagogastric junction line were staged as cT3 according to esophageal cancer staging; 2 cases with cancer epicenter locating > 2 cm below esophagogastric junction line were staged according to gastric cancer staging, of whom one was staged as cT3 due to regular serosa and the other was staged as cT4a due to irregular serosa. Postoperative pathology: 33 cases were pT3 and 10 cases were pT4a. The accuracy of preoperative CT in discrimination of T3 from T4a was 74.4%(32/43) with UICC/AJCC criteria and 65.1%(28/43) with IGCA criteria, whose difference was significant(P<0.01).

CONCLUSIONSPreoperative CT can accurately localize the 2 cm threshold line of Siewert II esophagogastric junction adenocarcinoma, which is beneficial to the discrimination of cT3 from cT4a EGJ adenocarcinoma. Application of the UICC/AJCC 8th edition criteria to above discrimination has higher accuracy as compared to IGCA 4th edition in cT-staging by CT.