[The analysis of unconventional lymph node metastasis in tongue squamous cell carcinoma]

Objective: To analyze the characteristics of cervical lymph node metastasis in tongue squamous cell carcinoma (TSCC). Methods: A retrospective study was conducted. A total of 329 patients with TSCC who underwent en bloc resection of primary tumor and neck dissection in the Second Xiangya Hospital of Central South University from June 2010 to March 2018 were included. There were 283 males and 46 females, aged from 26 to 80 years. All patients underwent the modified neck dissection. The main difference between the modified neck dissection and the traditional neck dissection lay in the managements of unconventional lymph nodes. The lymphatic adipose tissues adjacent to the superior thyroid artery, the base of facial artery and the branches of external carotid artery were thoroughly dissected. The primary tumor as well as lingual artery, tissues along the lingual artery and lymph nodes in the mouth floor were resected. χ² test was used for comparison of count data, and linear regression model was used for multivariate analysis. Results: Cervical lymph node metastases were found in 136 patients (41.3%). Among 142 patients (T1-2cN0) with supraomohyoid neck dissection, 22 patients had pathologically occult lymph node metastases (15.5%), with a 5-year overall survival rate of 90.2%, which was similar to the 5-year overall survival rate of 92.1% in 120 patients without lymph node metastasis (χ²=0.156, P=0.693). Multivariate linear regression analysis showed that T stage, clinical stage and unconventional lymph node metastasis were important factors for cervical lymph node metastasis in tongue cancer patients (P<0.05). Unconventional lymph node metastases occurred in 30 patients (9.1%), including the metastases of lymph nodes in the floor of mouth (3.0%), the lingual artery (2.4%), the base of the external maxillary artery (2.1%), the superior thyroid artery (0.9%), and the external carotid artery (0.6%). There were significant differences in the unconventional lymph node metastasis rates between patients with negative and positive conventional lymph node metastases [4.9%(10/203) vs. 15.9%(20/126), χ²=11.242, P=0.001] and also between patients with depth of invasion ≤5 mm, 5 mm 10 mm [3.1%(2/64) vs. 5.7%(6/106) vs. 13.8%(22/159), χ²=7.907, P=0.005]. Conclusion: Supraomohyoid neck dissection can achieve reliable control efficacy in patients with cN0 tongue cancer. All patients with lymph node dissection should undergo unconventional lymph node dissection. Unconventional lymph node dissection is strongly recommended for patients with conventional lymph node metastasis.