278. PROPOSED REVISION TO THE DESCRIPTION OF T3 FOR ESOPHAGEAL CANCER: REMOVAL OF “ADVENTITIA”
Authors: Shinohara Hisashi , Kurahashi Yasunori , Nakamura Tatsuro , Nakao Eiichiro , Hojo Yudai , Kohno Shugo , Murakami Motoki , Ishida Yoshinori 
Published: September 2024

Abstract

Background
T3 is an important depth for esophageal cancer to target for surgical cure. According to the Union for International Cancer Control (UICC), T3 is defined as tumor invading the adventitia. However, it remains unclear what structures the adventitia refers to. In fact, tumors that do not directly invade adjacent organs have been classified as T3, even if they extend through the adventitia. Furthermore, in tumors arising at the esophagogastric junction (EGJ), it is difficult to determine the border with the subserosa that defines T3 of the stomach. Our aim was to revise the description of T3 in esophageal cancer.

Methods
The Union for International Cancer Control T-classification was reviewed from a histologic, pathologic, and embryologic perspective. Analysis of endoscopic ultrasound images, review of intraoperative images, and detailed observation of surgical specimens were followed by a review of the literature.

Results
Histologically, the adventitia is the extramural adipose connective tissue of the digestive tract and serves as a conduit for blood vessels, lymphatics, and nerves. The esophageal adventitia is further surrounded by connective tissue of adjacent organs, such as the tissue around the trachea, the tissue around the descending thoracic aorta, the pulmonary ligament, and the tissue on the diaphragm (Fig. 1a). In the 2022 revision of the Japanese Esophageal Society, resectable borderline cases in which adjacent organ invasion cannot be excluded by preoperative imaging were subclassified as borderline resectable T3 (T3br). From another perspective, this is a clinically reasonable criterion that not only adventitial invasion, but also invasion of connective tissue associated with adjacent organs is classified as T3. Beyond the EGJ, the adventitia is covered by mesothelium in the peritoneal cavity and leads to the subserosa. Endoscopic ultrasound revealed the fatty tissue of the adventitia as a highly echogenic layer on the surface of the muscularis propria, which continues uninterrupted beyond the EGJ into the stomach, indicating that the adventitia is connected to the subserosa. Intraoperative images showed that the descending posterior trunk of the vagus nerve and its associated vessels pass through the adipose tissue surrounding the esophagus in the esophageal hiatus (Fig. 1b). Thus, the ambiguity in the T-classification of esophageal cancer is not resolved as long as T3 is defined by the adventitia. In practice, however, physicians may have classified tumors as T2 if confined to the muscularis propria, T4 if invading adjacent organs, and T3 if neither.

Conclusion
We suggest that the description of T3 esophageal cancer be revised to read "tumor extends through the muscularis propria" rather than using the term "adventitia". This revision would clarify the depth criteria for determining the indication for surgical treatment not only for esophageal cancer, but also for EGJ carcinoma where the tumor center overlaps the gastric side.