Discrepancy between cTNM and pTNM staging of oral cavity cancers and its prognostic significance

Introduction: Accurate tumor-node-metastasis(TNM) staging of oral cavity cancer(OCC) is very important in the management of this dismal disease. However, stage migration from cTNM to pTNM was found in a portion of OCC patients. The objective of this study was to determine the possible causes of discrepancy between cTNM and pTNM in OCC and the clinical impacts of stage migration. Methods: Clinical and pathological data of 252 OCC patients were retrospectively reviewed and compared each other. Clinical staging was determined through the multidisciplinary evaluation of pre-treatment work-ups including PET/CT. In addition, we compared the up-staged cases with those in the no-change group with the same pTNM stages to identify the clinical impacts of such change. Results: Clinical staging yielded overall 82.5% diagnostic accuracy in predicting pathological tumor status, and tumor extent was under-estimated in 9.5-13.5% of cases. The main causes of T up-staging were under-estimation of surface dimension (62.5%) and deep invasion to tongue extrinsic muscles (37.5%). N up-staging was due to occult single (57.6%) and multiple (42.4%) metastases. Surprisingly, TNM up-staging in our series did not have prognostic significance under the current management protocol. Conclusion: Clinical under-estimation of pathological tumor extent occurred in approximately 13% of OCC, without clinical impacts on prognosis.