Eighth edition of the American Joint Committee on Cancer staging system: are we getting closer to the ideal classification for gastric cancer?

For patients diagnosed with cancer, the outcomes are mainly determined by the stage of the disease; while it establishes the risk of progression and the median survival, it also serves as a guide when planning the treatment. Tumor extension and metastases to lymph nodes (LNs) have been proven as the most important prognostic factors; in this regard, the tumor-node-metastasis (TNM) classification is currently recognized as the standard tool for staging malignant solid tumors (1,2). Nevertheless, it is not a perfect system as it has limitations; specifically, in gastric cancer, the 7th edition was criticized for failing to incorporate the two N3 subclassifications into the final stratification despite reports of significant differences (1,3,4). The 8th edition published in 2017 included this key change to the pathologic grouping, dividing the N3 category into N3a (7–15 positive LNs) and N3b (≥16 positive LNs). As a result, stage shifts occurred: on one side, some tumors were upstaged (T1N3bM0 from IIB to IIIB, T2N3bM0 from IIIA to IIIB and T3N3bM0 from IIIB to IIIC); on the other hand, others were downstaged (T4aN2M0 from IIIB to IIIA and T4aN3aM0 and T4bN2M0 from IIIC to IIIB) (5). At first sight, this enabled a widening of the distance between the survival curves and therefore entailed an apparently better classification (2,6); however, the cohort of patients used in creating the new edition might not represent all the populations around the world, since 84.8% of the cases came from Japan and Korea and just 8.8% were from western countries (6)