Nodal Metastasis in Oral Squamous Cell Carcinoma: Predictive Impact of MRI-Derived Depth of Invasion According to the 8th Edition American Joint Committee on Cancer Staging System

Abstract

To evaluate the relationship between the magnetic resonance imaging (MRI)-derived depth of invasion (DOI) and nodal recurrence in clinically node-negative patients with oral squamous cell carcinoma (SCC). The institutional review board approved this retrospective study. The study population consisted of 90 patients with clinical T1-2N0 oral SCC classified according to the 7th edition American Joint Committee on Cancer (AJCC) staging system; 41 were staged as T1N0 and 49 as T2N0. They (55 males and 35 females; median age, 70 years; age range, 29 - 92 years) had undergone routine pretreatment radiological examinations including MRI and 18F-fluorodeoxyglucose (FDG)-positron emission tomography (PET)/computed tomography (CT) fused imaging. The clinical pretreatment stage had been identified at a routine preoperative conference; the radiological diagnosis of nodal involvement was based on accepted morphologic criteria and FDG uptake. The primary tumors were located in the buccal mucosa (n = 4), upper gingiva (n = 11), lower gingiva (n = 12), hard palate (n = 3), tongue (n = 52), and floor of the mouth (n = 8). All patients were treated with local resection alone as primary treatment and watchful waiting for neck management. We reviewed DOI on pretreatment MRI and reclassified T stage according to the 8th edition AJCC. During the median follow-up period of 36 months (range, 2 - 122 months), the initial sites of recurrence were classified as local, nodal, and distant. Using Student's t-test and Pearson's chi-squared test, the MRI-derived DOI and T stage according to the 7th and 8th editions were assessed as predictive factors for nodal recurrence. The MRI-derived DOI was recorded as ≤ 5 mm in 42-, 5-10 mm in 37-, and > 10 mm in 11 patients. According to the 8th edition, 22 tumors were T1, 61 were T2, and 7 were T3 stage. During the follow-up period, 11 and 16 patients, respectively, suffered local and nodal recurrence; there were no patients with distant recurrence. The mean (± standard deviation) value of the MRI-derived DOI was significantly higher in the patients with nodal recurrence (8.4 ± 2.4 mm) than the others (4.7 ± 3.4 mm) (p < 0.001). The MRI-derived DOI classified significantly different risk groups for nodal recurrence; the incidence was 2% for tumor ≤ 5mm, 27% for 5-10 mm, and 46% for > 10 mm (p = 0.001). T stage according to the 8th edition also predicted the nodal recurrence; the incidence was 0% for T1, 21% for T2, and 43% for T3 stage (p = 0.016). However, T stage according to the 7th edition was not a significant factor for the nodal recurrence; no factors predicted the local recurrence. The MRI-derived DOI can predict nodal metastasis and the information may assist in treatment planning for oral SCC.