A semi-quantitative World Health Organization grading scheme evaluating worst tumor differentiation predicts disease-free survival in oral squamous carcinoma patients

•Disease free survival was estimated in an oral squamous carcinoma cohort (N = 87).•WHO grading & pattern of invasion based histological schemes were examined.•For worst WHO grading, criterion for assigning grade-3 tumors was defined.•Grade-3 tumors as per worst WHO grading exhibited shorter time to recurrence.•Worst WHO grading and tumor size were independent predictors on multivariate tests.

We investigated World Health Organization (WHO) grading and pattern of invasion based histological schemes as independent predictors of disease-free survival, in oral squamous carcinoma patients. Tumor resection slides of eighty-seven oral squamous carcinoma patients [pTNM: I&II/III&IV-32/55] were evaluated. Besides examining various patterns of invasion, invasive front grade, predominant and worst (highest) WHO grade were recorded. For worst WHO grading, poor-undifferentiated component was estimated semi-quantitatively at advancing tumor edge (invasive growth front) in histology sections. Tumor recurrence was observed in 31 (35.6%) cases. The 2-year disease-free survival was 47% [Median: 656; follow-up: 14-1450] days. Using receiver operating characteristic curves, we defined poor-undifferentiated component exceeding 5% of tumor as the cutoff to assign an oral squamous carcinoma as grade-3, when following worst WHO grading. Kaplan-Meier curves for disease-free survival revealed prognostic association with nodal involvement, tumor size, worst WHO grading; most common pattern of invasion and invasive pattern grading score (sum of two most predominant patterns of invasion). In further multivariate analysis, tumor size (> 2.5 cm) and worst WHO grading (grade-3 tumors) independently predicted reduced disease-free survival [HR, 2.85; P = 0.028 and HR, 3.37; P = 0.031 respectively]. The inter-observer agreement was moderate for observers who semi-quantitatively estimated percentage of poor-undifferentiated morphology in oral squamous carcinomas. Our results support the value of semi-quantitative method to assign tumors as grade-3 with worst WHO grading for predicting reduced disease-free survival. Despite limitations, of the various histological tumor stratification schemes, WHO grading holds adjunctive value for its prognostic role, ease and universal familiarity.