Objective: More than 40% of patients with squamous cell carcinoma (SCC) of the floor of mouth present with lymph node metastasis (LNM) at the time of diagnosis. LNM is a poor prognostic factor, with the presence of even 1 positive lymph node associated with as much as 50% reduction in overall survival. It has been well-established that the extent of nodal involvement, as classified by the American Joint Committee on Cancer (AJCC) N staging system, correlates with decreased survival. Recent literature has suggested that the level of LNM may add prognostic value to AJCC N stage for estimating prognosis on the basis of nodal disease. This prognostic relationship has yet to be analyzed for SCC of the floor of mouth. Here we compare the prognostic significance of level of LNM and AJCC N stage for SCC of the floor of mouth, hypothesizing that the level of LNM is significantly associated with worsening survival.
Study Design: Cross-sectional analysis of the National Cancer Institute’s SEER database (Surveillance, Epidemiology, and End Results).
Methods: The SEER database was used to identify cases of SCC of the floor of mouth with LNM from 2004 to 2014. Level of LNM was categorized as primary (level I, II, III), secondary (level IV), or tertiary (level V) according to the frequencies of lymph node involvement (highest to lowest) for floor of mouth SCC, as has been done in prior studies. The sample was grouped by level of LNM and AJCC N stage and Kaplan-Meier curves were used to analyze rates of survival. A subset of patients with advanced disease (N2) was also analyzed to determine if the prognostic value of staging metrics varies based on the extent of nodal involvement.
Results: In total, 2179 patients with SCC of the floor of mouth were identified. Level I represented the most commonly involved nodal basin, followed by Level II and Level III. Level of LNM showed a significant effect on overall survival (OS) [5-yr OS: primary (29.2%), secondary (22.0%), tertiary (16.8%), P<.001] as did AJCC N stage [5-yr OS: N1 (34.4%), N2 (23.3%), N3 (20.5%) P<.001]. Among the subset of N2 patients, level of LNM and AJCC subclassification (N2a, N2b, N2c) were also both significantly associated with poor survival, again demonstrating similar patterns of worsening outcomes with higher groupings.
Conclusion: The level of LNM predicts worsening overall survival for patients with SCC of the floor of mouth and may add prognostic value to AJCC N classification for these tumors.