Tumour infiltration depth ≥4 mm is an indication for an elective neck dissection in pT1cN0 oral squamous cell carcinoma.

Patients with pT1cN0 oral squamous cell carcinomas (OSCC) are generally not treated with a neck dissection (ND). However, in 25% of cN0 patients, nodal metastases become apparent during follow-up. Infiltration depth of the primary tumour has been consistently associated with the presence of nodal metastasis, but proposed cut-off depths for performing a ND vary considerably. The aim of this study was to explore the infiltration depth as predictor for the nodal status and to recommend a cut-off depth for performing a ND. From our database of 351 primary oral carcinomas, we selected all pT1-2 tumours (n=246). Infiltration depth was measured in 212 cases. Neck status was determined by histopathological examination of the dissection specimen, or by at least two years of follow-up. Mean infiltration depth was 5.49 mm (95% CI: 4.86-6.12) in the N0 and 8.40 mm (95% CI: 7.38-9.43) in the N+ group (p<0.001). cN status, lymphovascular invasion and infiltration depth were the only independent predictors for nodal status in multiple logistic regression. ROC-analysis on pT1cN0 tumours resulted in an optimal cut-off for the prediction of the nodal status at a depth of 4.59 mm. This cut-off identified a subgroup of patients at increased risk for nodal metastasis (OR=8.3) and with significantly shorter survival. Tumour infiltration depth is an independent predictor for nodal status in pT1-2 OSCC. In pT1cN0 tumours, a cut-off at 4.59 mm results in the best predictive value. We recommend an infiltration depth of ≥4 mm as an indication to perform a neck dissection in pT1cN0 OSCC.