Factors associated with cervical lymph node metastasis in lower-lip squamous cell carcinoma: emphasis on depth of invasion and histopathological features

To identify factors associated with cervical lymph node metastasis in patients who underwent surgery for lower-lip squamous cell carcinoma (SCC). This retrospective study included patients who underwent surgical treatment for lower-lip SCC. Demographic, clinical, and histopathological characteristics including tumor size, depth of invasion (DOI), perineural invasion (PNI), lymphovascular invasion (LVI), and cervical lymph node status were evaluated. Fisher’s exact test was used for categorical variables, and the Mann–Whitney U test was used for continuous variables. Because of the small number of node-positive patients and complete separation for LVI, Firth’s penalized logistic regression was used for the multivariable analysis. The discriminative ability of DOI for cervical lymph node metastasis was assessed using ROC curve analysis, with a significance level of p < 0.05. A total of 73 patients were evaluated (mean age: 63.0 ± 11.8 years; male/female ratio: 61.6%/38.4%). Cervical lymph node metastasis was detected in 8.2% of patients. Nodal metastasis was significantly associated with increased DOI ( p = 0.004), PNI ( p < 0.001), and LVI ( p = 0.006). In the multivariable model, however, none of these variables (DOI, PNI, or LVI) reached statistical significance as independent predictors of nodal metastasis, likely reflecting the small number of node-positive cases. ROC analysis showed that DOI showed reasonable within sample discrimination for nodal metastasis (AUC = 0.848; 95% CI = 0.641–1.000; cutoff = 6.5 mm; sensitivity = 83%, specificity = 90%), although the wide confidence interval reflects the small number of node-positive cases. DOI, PNI, and LVI were significantly associated with cervical lymph node metastasis in lower-lip SCC in univariate analyses, although none remained independently significant in the multivariable model. Given only six node-positive cases and the absence of internal or external validation, these exploratory findings, including the 6.5-mm DOI cutoff, should not be used to guide surgical planning or elective neck-treatment decisions and require confirmation in larger, externally validated cohorts.