Discrepancies between UICC and AJCC TNM classifications for oral cavity tumors in the 8th editions and following versions

Purpose: To underline discrepancies between the Union for International Cancer Control (UICC) and the American Joint Committee on Cancer (AJCC) Tumor-Node-Metastasis (TNM) classifications in oral cavity cancer. Methods: Comparison between the UICC and AJCC TNM classifications of oral cavity cancer in their 8th editions and following versions. Results: The most important update was the introduction of the depth of infiltration (DOI), which reflects the proximity of the tumor to the underlying lymphovascular tissues and was associated to the presence of nodal metastases. Since the first publication of the 8th edition of the AJCC Cancer Staging Manual on March 30, 2017, two further versions have been published, while the UICC TNM classification was left unchanged until a document containing modifications to the 8th edition of the UICC TNM Classification of Malignant Tumours was published online on October 6, 2020. Conclusion: Different versions of the TNM classification can be confounding for the scientific community. Citing the 8th edition of the UICC TNM Classification of Malignant Tumours or the AJCC Cancer Staging Manual without specifying the precise version used for classification may be insufficient. Clinicians and researchers are invited to always refer to the latest update of each classification.