Clinical and Molecular Determinants of Malignant Transformation in Oral Epithelial Dysplasia

Known risk factors for malignant transformation in oral lesions with malignant potential include the size and appearance, however the importance of site, grade of dysplasia and exposure to environmental carcinogens remains controversial. Patients with a diagnosis of oral epithelial dysplasia (OED) were recruited to a longitudinal observational cohort study in a tertiary oral dysplasia clinic. Clinical, histopathological and risk factor data were assessed to identify clinical determinants of malignant transformation; in patients where the oral dysplasia underwent malignant transformation the treatment outcomes were evaluated. Ninety-eight eligible patients were recruited and followed up for the median duration of 48 months. Twenty-six (26.5%) patients underwent malignant transformation, with significant predictors as follows: non-smoking status, lateral tongue subsite, non-homogeneous appearance, high histological grade and size of lesion >200mm2. Whilst these clinical features have previously been associated with malignant transformation in OED, the highly statistically significant finding of malignant transformation in non-smokers, consistent with several cohorts reported in the recent years. This suggests that these patients, apparently with endogenous OED, perhaps with inherited or acquired predisposition, are considered to be at higher risk (compared to smokers) and should form the focus for further investigation. All 26 patients in whom dysplasia transformed to oral squamous cell carcinoma were presented to the multidisciplinary team (MDT) with stage 1 disease. Ninety-one percent (21/23) were initially treated by wide local excision and 9% (2/23) required tumour resection followed by reconstruction. Twenty-two percent (5/23) of patients developed second primary OSCC, and further diagnoses of oral dysplasia with an estimate that 76% of patients will undergo one or more event in 5 years. Specialist monitoring of OED by a multidisciplinary team allows detection of OSCC at an early stage, facilitating largely curative treatment with simple and usually minor surgical intervention. The high incidence of second primary OSCC formation in high risk patients with OED supports an intensive targeted surveillance regimen in this group of patients. The observed higher rate of malignant transformation in non (or light)-smokers supports the hypothesis of an endogenous aetiology. It is hypothesised that loss of FANCD2 and associated proteins lead to genomic instability and oncogenesis. Longitudinal archival samples were obtained from 40 individuals with OED from time of diagnosis to the most recent clinical review in 23 non-transforming/stable OED or until excision of the SCC in 17 unstable OED undergoing malignant transformation. Histopathological reassessment, immunohistochemistry for FANCD2 and Western blotting for phosphorylation/mono-ubiquitination status of ATR, CHK1, FANCD2 and FANCG were undertaken on each tissue sample. Immunohistochemistry studies found under-expression of FANCD2 was observed in the diagnostic biopsy of OED lesions which later underwent malignant transformation when compared with stable OED. Combining the FANCD2 immunohistochemistry scores with histological grading more accurately predicted malignant transformation (p=0.005) than histology alone and correctly predicted malignant transformation in 10/17 initial biopsies. A significantly reduced expression of total FANCD2, pFANCD2, pATR, pCHK-1 and pFANCG were observed in OED which underwent malignant transformation. There is strong evidence that defects in the DNA damage sensing-signalling-repair cascade are associated with malignant transformation in OED. Loss of post-translational modification in FANCD2 and related proteins, was more predictive of malignant transformation when compared to clinical parameters