Evaluation of Depth of Invasion and Tumor Thickness as a Prognostic Factor for Early-Stage Oral Squamous Cell Carcinoma: A Retrospective Study

Abstract

The aim of this study was to compare the effect of using depth of invasion (DOI) versus tumor thickness (TT) as a prognostic factor for early-stage oral squamous cell carcinoma (OSCC). A total of 57 patients with early-stage OSCC treated surgically from 2009 to 2014 at our institution were reviewed retrospectively. Histopathological measurement of DOI and TT was performed. The validation of DOI and TT as prognostic factors was conducted using a Kaplan-Meier survival analysis. TT had no association with disease-specific survival (DSS) or progression-free survival (PFS) in this cohort; however, increased DOI was significantly associated with decreased DSS but not correlated to decreased PFS. The T category of the 7th edition of AJCC was statistically associated with both DSS and PFS; however, the T category of the 8th edition of the AJCC was only associated with DSS. In this study group, TT could not be used as a prognostic factor, and DOI was not by itself sufficient to predict prognosis for early-stage OSCC. The T category in AJCC 8th Edition cannot be considered the sole prognostic factor for early OSCC, so additional prognostic factors may need to be considered.

Keywords: T category; depth of invasion (DOI); disease-specific survival (DSS); early-stage oral squamous cell carcinoma (OSCC); progression-free survival (PFS); tumor thickness (TT).

Figure 1

Measurement of depth of invasion (DOI) and tumor thickness (TT), using iSolution Lite software (2003–2015, IMT i-solution Inc., Vancouver, BC, Canada). Measuring was repeated three times for each slide, and the mean value was used as the final value. (×40, Blue line; tumor thickness, Red line; depth of invasion).

Figure 2

Kaplan–Meier curves showing disease-specific survival (DSS) and progression-free survival (PFS) stratified by depth of invasion (DOI): (A) DSS curves stratified by DOI. (A [DOI ≤ 5 mm], n = 30, B [5 mm < DOI ≤ 10 mm], n = 18, C [DOI > 10 mm], n = 9); (B) PFS curves stratified by DOI. (A [DOI ≤ 5 mm], n = 30, B [5 mm < DOI ≤ 10 mm], n = 18, C [DOI > 10 mm], n = 9).

Figure 3

Kaplan–Meier curves showing disease-specific survival (DSS) and progression-free survival (PFS) stratified by tumor thickness (TT): (A) DSS curves stratified by TT. (A [TT ≤ 5 mm], n = 19, B [5 mm < TT ≤ 10 mm], n = 28, C [TT > 10 mm], n = 10); (B) PFS curves stratified by TT. (A [TT ≤ 5 mm], n = 19, B [5 mm < TT ≤ 10 mm], n = 28, C [TT > 10 mm], n = 10).

Figure 4

Kaplan–Meier curves showing disease-specific survival (DSS) and progression-free survival (PFS) stratified by the T category of the 7th edition of the AJCC system: (A) DSS curves stratified by the T category based on the 7th edition of the AJCC. (T1, n = 35, T2, n = 22); (B) PFS curves stratified by T category based on the 7th edition of AJCC. (T1, n = 35, T2, n = 22).

Figure 5

Kaplan–Meier curves showing disease-specific survival (DSS) and progression-free survival (PFS) stratified by T category of the 8th edition of the AJCC system: (A) DSS curves stratified by T category (DOI) based on the 8th edition of the AJCC. (T1, n = 22, T2, n = 26, T3, n = 9); (B) PFS stratified by T category based on criteria of the 8th edition of the AJCC. (T1, n = 22, T2, n = 26, T3, n = 9).