Even microscopic extranodal extension has significant recurrent and metastatic potential in oral squamous cell carcinoma.

Purpose: Extranodal extension (ENE) in the metastatic lymph nodes of head and neck cancer is widely recognised as a high-risk factor for postoperative recurrence and metastasis. Major ENE (ENEma) cases have a poor prognosis; however, the potential for recurrence and metastasis in microscopic ENE (ENEmi) cases is unclear. Therefore, we aimed to analyse the characteristics of ENEma and ENEmi to verify the clinical and histopathological significance of ENEmi.

Methods: We included 170 patients with oral squamous cell carcinoma who underwent initial surgery at our institution between 2012 and 2020. Using a cut-off value of 2 mm, ENE cases were divided into the ENEma group (63 cases), ENEmi group (39 cases), and ENEn (ENE none; 68 cases). Prognosis and recurrence were compared between the three groups.

Results: There was a statistically significant decrease in the survival curve of patients with ENEma with respect to overall survival (OS) (p = 0.03). However, both ENEma and ENEmi groups showed similar curves for locoregional control (LRC) and distant control (DC). When comparing the ENEmi and ENEn groups, a statistically significant decrease in survival was observed for both LRC and DC (LRC, p = 0.02; DC, p = 0.01).

Conclusion: ENEmi tumours have significant recurrent and metastatic potential; therefore, histopathological detection of micrometastatic lesions is of great importance. The validity of postoperative treatment for ENEmi cases needs to be verified in further prospective studies.