Tumor depth of invasion versus tumor thickness in guiding regional nodal treatment in early oral tongue squamous cell carcinoma

Objectives. Tumor thickness (TT) and tumor depth of invasion (DOI) correlate with the risk of regional lymph node metastases in early oral tongue squamous cell carcinoma (OTSCC). We aimed to determine optimal cutoff points to guide elective nodal treatment in early OTSCC. Study Desin: This retrospective study included 145 patients treated between 1995 and 2012 for histologically proven OTSCC (<4 cm). The minimum P value method was used to calculate the cut-point values of TT and DOI that predicted for nodal disease. The utility of the DOI cut-point value and the 5-mm DOI currently used for staging were then compared. Results. Logistic regression analysis demonstrated that DOI (P=.00036) and TT (P=.0001) were highly correlated with nodal disease and each other. The cut-points that best predicted for nodal disease were 4.5 mm for DOI and 8 mm for TT. There was no difference in utility between DOIs of 4.5 mm and 5 mm. Conclusions. TT and DOI were highly correlated with nodal risk but had different cut-points for prediction. Our findings highlight the need to recognize these parameters as discrete entities and to report them appropriately. This study's findings support the use of the 5-mm DOI, currently used for staging, as also the threshold value to guide elective nodal treatment.