Immunohistochemical evaluation of Fhit protein expression in oral squamouscell carcinomas

The expression of Fhit (fragile histidine triad) protein in oral squamous c ell carcinoma (OSCC) and adjacent oral epithelium was evaluated by immunohi stochemistry on formalin-fixed paraffin-embedded blocks of 32 cases of OSCC . Rabbit polyclonal anti-GST-Fhit antiserum at 1:600 was used, after antige n enhancement in a microwave pressure cooker, in a saturated lead thiocyana te solution. This antiserum has been shown specifically to detect human Fhi t by immunohistochemistry at dilutions up to 1:10,000.The Fhit protein expr ession was evaluated using both the intensity and extent of staining. Norma l stratified squamous epithelium showed strong positivity, especially in th e stratum spinosum and areas of keratinisation. Basal and parabasal cells w ere negative or expressed low levels of Fhit relative to the squamous epith elium. Mild and moderate epithelial dysplasia showed Fhit expression in the superficial layers, while Fhit expression was absent from severely dysplas tic lesions. A reduction or loss of Fhit expression was found in 21 (66%) o f the OSCC. The alterations in Fhit protein expression in OSCC, and not in normal tissues, are consistent with the proposal that Fhit inactivation pla ys a role in oral carcinogenesis.