Clinical implication of the innovations of the 8^th edition of the TNM classification for esophageal and esophago-gastric cancer

Epidemiology of esophageal cancer and esophagogastric junction (EGJ) has deeply changed for the past two decades with a dramatically increase of adenocarcinoma whereas squamous cell carcinoma (SCC) has slowly decreased. Moreover, the two histological types differ in a number of features including risks factors, tumor location, tumor biology and outcomes. In acknowledgement of these differences, the newest 8^th edition of the American Joint Committee on Cancer (AJCC) tumor, node and metastasis (TNM) staging classification of epithelial cancers of the esophagus and EGJ has refined this histology-specific disease stage with incorporation of new anatomic and non-anatomic categories. Based on data-driven of patients collected through the Worldwide Esophageal Cancer Collaboration (WECC) group, the 8^th edition database encompasses a six-continent cohort of 22,654 patients among 33 institutions including patients treated with surgery alone and, for the first time, patients treated after neoadjuvant treatment. Anatomic categories include T descriptors (tumor invasion), N descriptors (regional lymph node invasion) and M descriptors (distant site). Non anatomic categories include grade differentiation (G descriptors) and tumor location (L descriptors). Category descriptors are currently assessed by endoscopy with biopsy, by endoscopy ultrasound fine-needle aspiration (EUS-FNA), by thoracic-abdominal-pelvic computed tomography (CT) and whole body flurodeoxyglucose positron emission tomography (FDG-PET) fused with CT. The new 8^th edition considers separate and temporally related cancer classification based on the treatment strategy: clinical cTNM (before any treatment), pathologic pTNM (after surgery alone) and postneoadjuvant pathologic ypTNM (after neoadjuvant treatment followed by surgery). The 8^th edition permits a more robust and reliable random forest–based machine learning analysis. Refinement of each T, N, M categories and subcategories makes the 8^th edition more accurate and more adaptable to the current practice including neoadjuvant regimen. The main objective of this review is to examine the current staging of esophageal cancer and the new aspects of the 8^th edition with its applications to clinical practice.