Depth of invasion versus tumour thickness in early oral tongue squamous cell carcinoma: which measurement is the most practical and predictive of outcome?

Abstract

The 8th edition of the American Joint Committee on Cancer (AJCC) Staging introduced depth of invasion (DOI) into the pT category of oral cavity squamous cell carcinoma. However, we noted multiple practical obstacles in accurately measuring DOI histologically in our daily practice. To compare the prognostic effects of DOI and tumour thickness (TT), a meticulous pathology review was conducted in a retrospective cohort of 293 patients with AJCC 7th edition pT1/T2 oral tongue squamous cell carcinoma. Overall survival (OS) and nodal metastasis rate at initial resection were the primary and secondary outcomes, respectively. We found that TT and DOI were highly correlated with a correlation coefficient of 0.984. The upstage rate was only 6% (18 of 293 patients) when using TT in the pT stage compared with using DOI. More importantly, DOI and TT, as well as pT stage using DOI and pT stage using TT, performed identically in predicting risk of nodal metastasis and OS. We therefore propose to replace DOI, a complicated measurement with many challenges, with TT in the pT staging system.