Background: Multiple recent studies have demonstrated that the number of lymph nodes removed during neck dissection is an independent predictor of survival for oral cavity squamous cell cancer. There is increasing interest in using lymph node yield as a quality metric in head and neck surgery, however it is not well understood what factors influence the number of lymph nodes identified in surgical specimens.
Methods: Retrospective review including patients with oral cavity squamous cell carcinoma undergoing neck dissection between January 2016 and June 2018. Collected variables included age, gender, race, ethnicity, BMI, history of chemotherapy, neck radiation or surgery, smoking status, number of lymph node levels dissected, experience of assisting resident, assistance by a fellow, tumor subsite, high risk tumor features such as perineural invasion, and pathologist. The primary clinical endpoint was lymph node yield. A protocol to histologically evaluate adipose tissue in neck dissection specimens was initiated by the pathology department at our institution in December 2017. The impact of the pathology protocol and other variables on lymph node yield was assessed. Group comparisons of the total lymph node yield were performed using Kruskal Wallis or Mann-Whitney U-tests, as appropriate. A generalized linear model with a gamma distribution and log link function was used to further analyze the total lymph node yield while controlling for possible confounding variables that were selected based on a univariate p value of <.10.
Results: Multivariable analysis included 187 patients. The median lymph node yield was 25 (IQR=15-38.25). Utilization of the pathology protocol was associated with an increase in lymph node yield, with an effect ratio of 1.214 (95% CI: 1.041-1.415; p=0.013). Multivariable analysis additionally demonstrated positive associations between lymph node yield and number of dissected lymph node levels (p<0.001), presence of at least one positive lymph node (p=0.005), and BMI greater than 25 (p=0.006). Prior neck surgery (p=0.001), prior neck radiation (p<0.001), and age 65 or greater (p=0.047) were negatively associated with lymph node yield. Assistance by a fellow was included in the model based on univariate p value of 0.055 but was not statistically significant in multivariable analysis (p=0.414). The pathology protocol was not associated with an increased number of positive lymph nodes in univariate analysis (p=0.346). Other studied factors did not demonstrate significant associations with lymph node yield.
Conclusion: Lymph node yield in neck dissection is influenced by many factors related to patient characteristics, prior treatment history, and treatment factors including those pertaining to both surgeon and pathologist. Many of these elements are not effectively captured in data from large database studies and should be considered in discussions of lymph node yield as a quality metric. Collaboration with the pathology department is essential to ensuring accuracy of specimen assessment and may independently increase lymph node yield in neck dissection.