External validation of the AJCC Cancer Staging Manual, 8th edition, in an independent cohort of oral cancer patients

Objectives: To evaluate the new American Joint Committee on Cancer (AJCC) cancer staging manual (8th edition) in an independent cohort of patients surgically treated for oral squamous cell carcinoma in order to determine whether the upstaging of pT and pN classification was indicative of a worse prognosis. Methods: A cohort of 298 patients was analyzed retrospectively. Results: Of these patients, 22.8% received an upstaging when the depth of invasion was included into the pT classification. Similarly, 29.2% of them were upstaged when extracapsular extension was added to pN classification. Twenty-eight of 68 patients (41.2%) that received an upstaging of pT classification died, and 23 (33.8%) experienced disease recurrence compared to 98/229 (42.8%) and 68/229 (29.7%), respectively, for those with the same pT during follow-up. With regard to pN classification, 70.6% of upstaged patients (60/85) died, and 50.6% (43/85) developed recurrence of the disease compared to 63/205 (30.7%) and 42/205 (20.5%), respectively, for those with the same pN during follow-up. Patients who were upstaged in pT classification presented a worse DFS (51.1% versus 80.4%, P = 0.007) and OS (31.5% versus 58.6%, P = 0.017). Similarly, those that were upstaged in pN classification presented a worse DFS (17.1% versus 61.2%, P = 0.001) and OS (8.5% versus 37.9%, P < 0.001). Conclusion: The new AJCC cancer staging manual (8th edition) allows a better stratification of oral SCC patients. By including the depth of invasion to the pT classification and extranodal extension to the pN classification, a worse disease-free and overall survival was assessed for these patients.