Retrospective observational study of occult cervical lymph-node metastasis in T1N0 tongue cancer

Objective: Delayed neck metastasis is the most significant prognostic factor for early tongue cancer. The main strategies for controlling cervical lymph nodes in Japan are elective neck dissection or watchful waiting. Elective neck dissection offers significantly better survival, but adversely impacts patient quality of life; consequently, here we investigated how to identify high-risk patients warranting elective neck dissection. Methods: We retrospectively evaluated 67 patients with T1N0 oral tongue squamous cell carcinoma who underwent primary treatment in our department from April 2001 to March 2015. All the patients underwent watchful waiting alone for neck management. We investigated the rates of occult neck metastasis, prognosis and circumstances of recurrence, and associations with pathological tumor thickness, depth and muscle invasion by the primary tumor. Correlation between the thickness in pathological specimens and that at magnetic resonance imaging was additionally investigated. Results: Neck recurrence was evident in 20 patients, of which 19 developed within 1 year. Therefore, the rate of occult neck metastasis was 29.9%. Patients with muscle invasion, tumor thickness >= 2 mm or tumor depth >= 2 mm on surgical specimens were significantly more likely to develop delayed neck metastasis. Prognosis was significantly worse for patients with muscle invasion or tumor thickness >= 2 mm. Thickness using magnetic resonance imaging was well correlated with pathological thickness. Conclusions: Patients with tumors >= 2 mm in thickness or muscle invasion developed neck metastasis, suggesting that elective neck dissection may be warranted for patients with these findings. For preoperative assessment of the need for elective neck dissection, magnetic resonance imaging would be a potential modality for T1N0 tongue cancer.