CHANGES OF MUTANT-TYPE P53 EXPRESSION IN SQUAMOUS-CELL CARCINOMA OF THE HEAD AND NECK DURING RADIATION-THERAPY AND ITS CLINICAL-SIGNIFICANCE - COMPARISON OF AN IMMUNOHISTOCHEMICAL METHOD AND PCR-SSCP ASSAY

P53 has been reported to be one of tumor suppressor genes that play a major role in signal transduction following many kinds of stresses, in cluding ionizing radiation. Changes in p53 expression during radiation therapy in tumor tissues have not yet been reported. We determined wh ether radiotherapy changes p53 expression in human squamous cell carci nomas of the head and neck, and established the possible correlations between p53 expression and the therapeutic effects of radiation therap y. 30 patients with tumors of the oral cavity, oropharynx, and maxilla ry sinus were examined, and all the tumors were confirmed as squamous cell carcinomas. Biopsies were performed on the cancer tissues before treatment and at doses of 4, 10, and 20 Gy of radiotherapy, and the sp ecimens were preserved in liquid nitrogen for further examination. Sam ples were immunohistochemically stained using streptoavidin-biotin per oxidase method and a monoclonal antibody against p53 (Ab-3, mutant typ e). For all the samples p53 PCR-SSCP (polymerase chain reaction-single strand conformation polymorphism) assays were performed. 14 of the 30 patients with squamous cell carcinomas showed expression of p53 in th eir tumor cells before and/or at 4 Gy or 10 Gy of radiotherapy. Eleven of the 14 tumors showed high radiosensitivity. Results of the p53 PCR -SSCP assays revealed mutations of p53 in 13 of 30 patients examined, and percentages of mutated p53 DNA varied at radiation doses of 4 Gy a nd 10 Gy. Ten of 12 patients with mutated p53 in their tumors showed d ecreased percentages of mutated p53 DNA during radiotherapy. The relat ionship between the immunohistochemical findings and the antitumor eff ect of a radiation dose of 20 Gy was examined on the correspondent hem atoxylin-eosin sections. In patients whose p53 expressions in tumor ce lls were grades + or ++ or +++ before radiotherapy and/or at 4 Gy of r adiotherapy, the tumors responded significantly well to radiation ther apy but the patients responded with significantly unfavorable clinical courses. The high radiosensitivity of squamous cell carcinomas in our samples could be explained by an overexpression of mutant type p53 in the tumor cells, and these mutant type p53-positive tumor cells possi bly showed radioresponsiveness.