S-phase fraction and DNA ploidy in oral leukoplakia

The risk of malignant conversion in oral leukoplakia is well documented. Histological findings are often unreliable and it is difficult to predict on the basis of clinical and histopathological changes which leukoplakic lesion will turn malignant.

We used the technique of flow cytometry to evaluate the ploidy status, DNA index and S-phase fraction in leukoplakia, oral cancer and normal oral mucosal biopsies and compared it with histological findings. The study was carried out on 30 patients with oral cancer, 60 with leukoplakia and 30 with normal oral mucosal biopsies.

The aneuploidy rate in oral cancers was 64%, for leukoplakia 20%, while all normal mucosal biopsies were diploid. Aneuploid lesions also had a greater S-phase fraction (SPF). The DNA Index (DI) of aneuploid oral cancers was 1.72 and aneuploid leukoplakias was 1.24. Leukoplakia specimens which showed histological evidence of dysplasia had aneuploidy rate of 38%, DI of 1.19 and SPF of 6.2%. The corresponding values for leukoplakia specimens without dysplasia were 14%, 1.09 and 4.1%, respectively.

The method of flow cytometry can be used to identify the subset of leukoplakia patients who are at a higher risk of malignant conversion. These patients could undergo more rigid surveillance or undergo excision biopsy of their lesions.