Comparative molecular and histological grading of epithelial dysplasia of the oral cavity and the oropharynx

Abstract

Histological grading of epithelial dysplasia in the oral cavity and oropharynx is used to predict the risk for cancer and to determine the treatment strategy. This grading, however, is subjective and not well reproducible. Recent publications have shown that molecular markers are promising in cancer risk assessment. The aim of the present study was to compare classical histological and molecular grading and to relate these to the proliferation rate by quantitative assessment of Ki-67 staining. Forty-three samples were analysed from the margins of patients who had undergone resection of their squamous cell carcinoma in the oral cavity/oropharynx. Three experienced pathologists performed the histological grading. With the consensus score, 12 samples were classified as normal and 31 as dysplastic (21 mild, six moderate, and four severe). Loss of heterozygosity (LOH) was assessed in the same samples with 15 microsatellite markers at chromosomes 3p, 9p, 17p, 8p, 13q, and 18q, and was present in 28 of the 43 samples. Twenty-four of the 28 cases (86%) with LOH were classified as dysplastic and four as normal. All ten samples with moderate and severe dysplasia and 14 of 21 samples with mild dysplasia contained LOH. In four of 12 biopsies classified as normal, LOH was found. A very striking and significant difference of the Ki-67 index was observed between LOH-positive and LOH-negative cases, 36.6 +/- 11.1% versus 19.4 +/- 2.8% positive cells, respectively. In mild dysplasia, 13 of 14 lesions containing LOH had a higher Ki-67 index than all seven lesions without LOH. Thus, in the oral cavity/oropharynx, LOH is more frequently found in the histologically higher-grade lesions (moderate dysplasia or worse) and in the lower grade lesions when a high proliferation rate is present. Assessment of proliferation with Ki-67 is a better surrogate for LOH than histological grading.