Evaluation of Depth of Invasion as a Histologic Predictor of Neck Node Metastasis in Squamous Cell Carcinoma of the Oral Tongue

The AJCC 8th edition has included depth of invasion as per the new CAP guidelines as an independent measure of T staging irrespective of tumour size. This aim of this study was to look at the correlation between depth of invasion measured by the new guidelines and neck nodal positivity rate in cases of carcinoma of the tongue. We performed a case series analysis of 131 cases of carcinoma tongue who underwent wide excision and neck dissection at a tertiary cancer care centre in North Kerala, India. Depth of invasion was reported as per the new CAP/AJCC guidelines and its correlation with lymph node positivity rate was assessed. We also looked at the upstaging caused by the addition of depth of invasion to T staging in the AJCC 8th edition. Lymph node positivity correlates well with depth of invasion, and the coefficient of correlation was 0.89 in our study. The lymph node positivity rate exceeded 15% when the depth of invasion exceeded 4 mm. 59.5% of T1 tumours and 28.5% of T2 tumours were upstaged when AJCC 8th edition TNM staging was used instead of 7th edition. Depth of invasion correlates well with lymph node positivity and the addition of depth of invasion in AJCC 8th edition results in upstaging compared to AJCC 7th.