Effect Of Depth Of Invasion Of Oral Squamous Cell Carcinoma On TNM Staging And Prognostic Evaluation

Objective:The 8th edition of the TNM staging manual was released by the American Joint Cancer Committee and the Union for International Cancer Control in January 2017.There are significant changes in the 8th edition of the TNM staging manual compared with the 7th edition,including increasing the depth of invasion and extranodal expansion.The purpose of this study was to analyze the effect of depth of invasion of oral cancer on TNM staging and prognosis evaluation,and to compare the significance of TNM staging system 8 and 7 in clinical treatment decision-making,prognosis stratification and improving the accuracy of prognosis evaluation of oral cancer.Methods:Patients with primary oral squamous cell carcinoma treated by oral and maxillofacial surgery in the Affiliated Hospital of Qing Dao University from January 2009 to June2015 were collected.The tumors were staged by TNM staging system of version 7 and 8respectively,and the changes of the two stages were compared.The statistical analysis was conducted by SPSS 26.0 software,Survival curves were performed with Kaplan-Meier method,the difference between survival curves was tested by Log-rank test.Harrell concordance index and the Akaike Information Criterion of each staging system were calculated,and the prediction accuracy and fitting data of the two staging models were compared.The ROC curve was used to calculate the Youden Index.The maximum value of the Jordan index was taken as the best DOI boundary value for predicting lymph node metastasis and survival.The hazard ratio was calculated by Cox proportional hazard model.P<0.05 was considered as the significant difference criterion.Results:The 570 patients who met the inclusion criteria included 388 males and 182 females,with an average age of 63.4.The median follow-up age was 64 years old(24～91 years old),and the median follow-up time was 38 months(2～135 months).The largest number of patients with squamous cell carcinoma of the tongue was 174,accounting for about 30.5% of the total number of patients.Squamous cell carcinoma of the floor of mouth and the gingiva ranked second and third,accounting for 27.2% and 23.3%.The 8th edition staging system changed the T staging of 190 patients,and the overall TNM staging of the original tumor was changed in 146 patients.The overall survival and disease specific survival models of T staging and TNM staging were analyzed by Log-rank test,P < 0.05.The difference between survival curves was statistically significant,and the Akaike Information Criterion of the 8th edition of the predictive model were lower than those of the 7th edition,and the concordance index was higher than that of the 7th edition,P < 0.05.The survival analysis after standard stratification of depth of invasion showed that the higher the grade of depth of invasion,the lower the survival rate.The difference between survival curves was tested by Log-rank test,P <0.05.In patients with squamous cell carcinoma of the floor of mouth,retromolar trigone and anterior tongue,the area under the curve of ROC used to predict lymph node metastasis,overall survival and disease specific survival analysis was more than 0.5,P < 0.05,which was statistically significant and had certain diagnostic value.The factors that might affect the prognosis of the disease were univariate analyzed and multivariate analyzed by COX proportional hazard model,which illustrating depth of invasion,lymph node metastasis and extranodal expansion were significantly correlated with the prognosis,especially in patients with more advanced grade.Conclusions:Depth of invasion and extranodal expansion were added in the AJCC 8th edition TNM staging of oral cancer,which changed the pathological staging of many patients according to the original standard staging.In this study,survival models were constructed by AJCC 7 T and TNM staging system and AJCC 8 T and TNM staging system respectively.AJCC 8 model is more accurate in evaluating prognosis,and the predictive ability of AJCC 8 model is higher than that of AJCC 7 model.Therefore,in clinical work,it is recommended to choose the new version of TNM staging system.According to the standard survival analysis after stratification,the survival rate of patients decreases with the increase of the stratification grade,and the depth of invasion can be used as an independent predictor to evaluate the prognosis of the tumor.it is recommended to consider this index when evaluating the prognosis of the disease.When the depth of invasion of the tumor in the floor of the mouth is ≥ 3.5mm,the diagnosis and treatment plan of cervical lymph nodes should be paid attention to and considered.When the depth of invasion of anterior tongue squamous cell carcinoma reaches 6.25 mm,the treatment of cervical lymph nodes is recommended.The clinical depth of invasion determines the formulation of diagnosis and treatment plan.For the evaluation of clinical depth of invasion of oral squamous cell carcinoma mainly involving soft tissues,such as carcinoma of the floor of mouth and anterior tongue,neck contrast-enhanced magnetic resonance scan is the preferred clinical choice.For tumors involving bone invasion,neck computed tomography enhanced scan or positron emission tomography/computed tomography(PET-CT)is recommended.Enhanced CT scan or PET-CT is a reliable method to evaluate the presence of bone invasion and destruction of tumors and extranodal expansion.According to COX proportional hazard model and AJCC 8 TNM staging system,patients with high risk of death and poor prognosis were classified as late stage Ⅳ,and the risk of death of patients with advanced ⅣB staging was significantly lower than that of AJCC 7,which proved that AJCC 8 TNM staging system was a more accurate death risk assessment model than AJCC 7 TNM staging system,and some patients with advanced ⅣB tumors should no longer be classified as very advanced tumors for treatment.